In his first appearance, "Mr. Monk Meets Dale the Whale" Biederbeck is the primary suspect in the slaying of a judge who issued a costly antitrust ruling against him. Several clues point to his being the killer, but it seems impossible because he is incapable of leaving his bedroom. It is also revealed in this episode that Monk harbors a severe hatred of Biederbeck, who sued his late wife Trudy and her newspaper after she wrote an unflattering article about him (calling him the "Genghis Khan of world finance"). Unlike many rich men, Biederbeck goes to extreme lengths to avoid publicity. He sued Trudy and the paper that published the article in a drawn-out libel suit that he knew he couldn't win, just to torment her. The legal costs forced the Monks to sell their first home, which Biederbeck snapped up and which he now claims to use to store his collection of pornography. Because Trudy was killed a short time later, Monk feels that Biederbeck stole one of the last years of her life. However, at the end of the episode, Monk proves that Biederbeck and his personal doctor conspired to kill the judge, and the doctor promptly turns state's evidence on Dale.

Biederbeck reappears in Season Two's "Mr. Monk Goes to Jail." Although he's been convicted of murder, he is adjusting to life in prison quite easily. He has an inmate to act as his personal servant, luxurious furniture, a TV, and just about everything one would not normally find in a prison environment — except a window. After a condemned prisoner is poisoned less than an hour before his execution, suspicion falls on Biederbeck, to whom the dead man owed $1,200. Both he and Monk know that Biederbeck wouldn't kill anyone over such a petty sum (as he says with a laugh, "I wouldn't bend down to pick up $1,200, even if I could"), but until the killer is caught, the prison is refusing to install Biederbeck's window. He offers Monk a deal: find the killer, and Biederbeck will share what he knows about Trudy's murder.

Even though Sharona tells him not to, Monk takes the case on the off-chance that Biederbeck is telling the truth. After Monk solves the case, Dale reveals that Trudy was, contrary to Monk's belief, indeed the intended victim of the car bomb. He also states that Monk should look for a man named Warrick Tennyson who can be found in Manhattan, New York. This gives Monk his first real lead on Trudy's death. The episode ends on an ominous note, as Biederbeck watches Monk's plane depart for New York through his newly installed window and smiles, "Bon voyage, Mr. Monk."

In the Season 3 premiere, Monk finds Tennyson, who confesses to being hired to kill Trudy, and identifies the man who hired him as having a six-fingered hand. To Sharona's, and even Monk's surprise, it's evident that Biederbeck was telling the truth after all.

The reason becomes clear in the two-part episode "Mr. Monk Is On The Run," when Monk is framed for murder of the six-fingered man who hired Tennyson. Dale is revealed to be the mastermind of the plot, and of a simultaneous plot to murder the Governor of California. The Lieutenant Governor, who is on Dale's payroll, would then pardon Dale, completing Dale's revenge by setting him free and putting Monk in jail. But Monk foils Dale's plan, and a corrupt sheriff who had been responsible for framing Monk turns state's evidence. As a result, all of Dale's privileges are revoked at the prison: His custom bed, telephone, and laptop are confiscated; special meal deliveries, manicure appointments, and his window is removed; and he is reduced to sleeping in a cramped bunk bed, with only a wheelchair to move around in and eating prison food in the cafeteria with the other inmates.

Biederbeck also makes a brief appearance in the novel "Mr. Monk Goes to Germany," by Lee Goldberg. Monk telephones Biederbeck from Germany when he suspects that one of Dr. Kroger's colleagues, a psychiatrist with a six-fingered hand, is the man who killed Trudy. Since the doctor was giving a lecture at Berkeley in the same week Trudy was killed, thanks to a grant from one of Biederbeck's foundations, Monk suspects Biederbeck of being the killer. Biederbeck smugly refuses to confirm or deny Monk's suspicions, but later Monk proves that the doctor is not Trudy's killer (the novel was written before, but published after, the airing of "Mr. Monk Is On The Run," and Goldberg's foreword acknowledged the discontinuity).

Trudy Anne Monk (Stellina Rusich) (Melora Hardin) is Monk's deceased wife. Her husband's attempt to solve her murder is the show's longest-running plot arc. She has formerly been played by Stellina Rusich during the first and second seasons, and Hannah Contrucci as young Trudy during fourth season. Lindy Newton plays Trudy in a college flashback in the fifth season.

Trudy Monk was born in Los Angeles in 1962.^[1] She attended the Ashton Preparatory School and graduated valedictorian in 1977 at the age of 15. She did not date very much while there, expecting to know who the right man would be once she found him.^[2] She graduated from the University of California, Berkeley. She met her future husband Adrian while he was working there at the library.^[3] Adrian and Trudy married on August 8, 1990.

In 1993, Trudy was involved in a lawsuit with financier Dale Biederbeck (a.k.a. Dale the Whale) because she referred to him as the "Genghis Khan of Finance". The Whale was unable to win the lawsuit, but the Monks were forced to sell their house paying for their lawyer. Adrian harbors an intense hatred for the Whale because of the pain he caused Trudy, saying that he stole five years of her life. The Whale remains an important adversary of Adrian's, especially when it is revealed that he had a role in Trudy's death. Adrian later proves the Whale guilty of murder and sees him jailed.

In Adrian's words, Trudy "enjoyed poetry, was often barefoot, and kept every promise she ever made". In "Mr. Monk Takes Manhattan", Adrian offers a glimpse into her mindset by turning Warrick Tennyson's morphine back on after he had turned it off.

Trudy Monk was murdered on a snowy^[4] December 14, 1997^[5] with a bomb containing 3 lbs of plastic explosives powered by 10 20V magnesium batteries that detonated under the front seat^[6] while she was on an errand to get cough medicine for Adrian's brother Ambrose.^[7] Ambrose blames himself for Trudy's death, and his guilt led to a 7-year rift between the brothers.

In "Mr. Monk Can't See a Thing", Adrian reveals that Trudy lived for 20 minutes after the bomb went off. Her last words to a paramedic were "bread and butter", a message to Adrian meaning that she would never leave him, as this was something she always told her husband when they had to temporarily let go of each other for some reason or another.

The bomb was built by Warrick Tennyson. Tennyson was hired by a six-fingered man whom he could not identify.^[8] Since the homicide's occurrence, Adrian had believed all along that he was the intended target, with Trudy being an innocent victim. The intense guilt contributed to and intensified his nervous breakdown, his obsessive-compulsive manifestations, and his bizarre phobias. In "Mr. Monk Goes to Jail", Dale the Whale reveals that the car bomb was actually intended for her, not him. Discovering that Trudy was the true target, Adrian is seen to be visibly affected by this piece of news. In "Mr. Monk Bumps His Head", Adrian attempts to find this 6-fingered man by purchasing a picture of him. The picture turns out to be a fake. In "Mr. Monk and Mrs. Monk", Natalie overhears a woman who looks like Trudy say that she faked her own death to protect Adrian. Adrian begins to believe this might be true, but in the end, it turns out that this woman has attempted to pass herself off as the real Trudy in order to get the key to Trudy's old storage unit.^[9] In "Mr. Monk Is Up All Night", Adrian sees a Brazilian woman whom he chases for several blocks for no apparent reason. At the end of the episode, it is revealed that the reason he was drawn to her is that she received a cornea transplant from an organ donor, who turned out to be Trudy.

Ambrose Monk, played by John Turturro, is the brother of Adrian Monk. He suffers from agoraphobia. He can be seen in person in three episodes, "Mr. Monk and the Three Pies", "Mr. Monk Goes Home Again" and "Mr. Monk's 100th Case", as well as in home movies as shown in Mr. Monk Is on the Air. He has a romantic interest in Natalie Teeger, Adrian's assistant. Ambrose writes owner's manuals for many different consumer products in multiple languages which he taught himself. The house he lives in is cluttered with his work, piles of newspapers, and filing cabinets which are stuffed with his father's mail spanning the entirety of his father's absence.

He blames himself for the death of Adrian's wife, Trudy. At Ambrose's request, Trudy was out buying him cough medicine when she was murdered by a bomb planted under the front seat of her car. Guilt-ridden, Ambrose avoided all contact with Adrian for seven years after the incident.

When Adrian and Ambrose were children, they shared a strong bond with their father. This may have been due to his strict rules, such as not ever entering his office, and the boys' social seclusion, causing a sort of dependency. In the episode 'Mr. Monk meets his Dad', Jack Monk explains to Adrian in his truck that he opened up a fortune cookie which said 'Stand by your man', so he followed his own path and left. Ever since, Ambrose has been obsessed with the idea of his return, even to the point of preparing a dinner plate for him every night, just in case. Adrian feels differently, believing his father will never return. However, their father showed up at Ambrose's doorstep to leave a note. Adrian and Ambrose, who were in an ambulance at the time due to the fact that they thought he had been poisoned by a Neptune candy bar, missed their father's appearance but the note congratulated Ambrose on finally leaving the house. Ambrose has left the house two other times: when it was on fire, and the second when he was visiting Trudy's grave (in the same episode).

In "Mr. Monk's 100th Case" he appears in a documentary about Adrian, and says his brother held the family together after Jack Monk left them. Both himself and his mother became unable to deal with the outside world, and Adrian Monk saved them (likely by being able to go to school and go shopping for needed items, like groceries). He greatly respects his brother's ability to cope with the outside world.

Jack Monk, played by Dan Hedaya, is Monk's father. He appears in the episode entitled "Mr. Monk Meets His Dad". Jack, the father of both Ambrose and Adrian Monk, abandoned his young family while running to pick up an order of Chinese food. Adrian was only eight years old and his father's abandonment is seemingly the catalyst for both Adrian and Ambrose's psychological illnesses. After leaving, Jack isn't heard from for over forty years. During that time he fathered yet another son, 31 year old Jack Jr. whom Jack proudly brags about to his co-workers as a genius doctor (but later admits to Adrian's surprise that Jack Jr. is an unemployed buffoon who smokes marijuana all day and steals money from his wallet). Jack finally makes an appearance - albeit an unnoticed one - at Ambrose's door to leave him a congratulatory note on Ambrose's exit from the house (though this was because he was being driven to the hospital in an ambulance at the time, having eaten what he thought was a poisoned candy bar).

Very little is known about Jack Monk's personal history. It is established by Adrian in the above-mentioned episode that Jack wrote school textbooks as his career of choice (similar to his other son, Ambrose), indicating some level of education. Not much explanation is provided for how he ends up in the state explored in "Mr Monk Meets His Dad."

When Jack finally shows up in person, he is working for a Midland, Texas-based trucking company and had been stopped in San Francisco for running a red light. He was arrested and was placed in jail for shoving the police officer who had stopped him. Initially, Adrian's reception to his father was icy and uninviting, but the two later reconciled over a road trip.

Jack Monk Jr. (Steve Zahn) is Monk's half-brother. His father (and Monk's father) left him and his mother after 10 years when their family was together. Jack Monk Jr. met Monk after he was arrested and imprisoned for attempting to sell cars that weren't his. He escaped from prison, but was framed for a murder right after. Jack went to his half-brother, Monk, in hopes that Monk could clear his name.

Jack Monk Jr. appears to be a pathological liar, and often swears "hand to God" that he is telling the truth when he really is not. He also has an obsession with the country of Paraguay, suggested to be due to the country's supposed lack of an extradition treaty with the United States.

His name was cleared and he went back to prison, though Randy's handcuffs "went missing".

Harvey Disher is Lt. Disher's late uncle who dies in season 5 episode "Mr. Monk Visits A Farm". Interestingly, it was mentioned that Lt. Disher only has aunts in the episode "Mr. Monk Gets Cabin Fever" in season 3, and also in "Mr. Monk vs. The Cobra", season 3.

Kevin Dorfman (Jarrad Paul) was Monk's annoying, talkative (according to Monk, "one time, he had a sore throat, he talked for two and a half hours about how much it hurt him to talk") upstairs neighbor until he was killed in "Mr. Monk and the Magician." He was often seen cooking (with Monk). He first appeared in Mr. Monk and the Paperboy, where he won $43 million in the lottery, although his "girlfriend" tried to hide it from him with the object of eventually getting it all. However he lost it all on bad investments, golddiggers, and sleazy accountants. A CPA, he had two sisters and could recall all eight times he ate egg salad sandwiches. Kevin worked in a coffee shop in Aspen, Colorado and accompanied Monk when his father-in-law asked him to investigate a cheating problem on a game show. According to Kevin, a pencil with chew marks on it is a "collectible". An amateur magician, he is killed the night of his professional debut in the episode "Mr. Monk and the Magician," by strangulation, due to his suspicion of a fellow magician's drug trafficking.

Benjamin "Benjy" Fleming is the son of Sharona Fleming. He was played by Kane Ritchotte in the pilot and second season and by Max Morrow in the rest of the first season, excluding the pilot. This is because Ritchotte lives on the west coast, where the pilot was filmed (in Vancouver) and where the second season was filmed (in Los Angeles), while Morrow lives on the east coast, where the remainder of the first season was filmed (in Toronto).

Monk bonds with Benjy but has his problems in relating since he never did the things normally associated with kids growing up. As a result he is clueless in giving Benjy a pep talk about baseball (Mr. Monk Goes to the Ballgame) since Benjy has to show him how to hold a bat. In Mr. Monk and the Playboy when Sharona tells him of her less than reputable past which was about to be revealed if Mr. Monk persisted in his investigation even though she knew Benjy would be open to ridicule and perhaps even lose respect for her, Benjy reassures her that he could handle it.

He is in little league ("Mr. Monk Goes to the Carnival"). He is a sixth-grader and wants to be a writer ("Mr. Monk Takes a Vacation"). He eventually returned to New Jersey with his mother to reunite with his father, Trevor Howe. His first appearance in any Monk-related story since he and Sharona left the television show was in the Lee Goldberg novel Mr. Monk and the Two Assistants, where Sharona returns to San Francisco because her husband was accused of murder. Benjy and his mother were mentioned in "Mr. Monk Is On The Run, Part 2," having sent flowers for the presumed deceased Monk and flying in to attend his funeral.

Linda Fusco (Sharon Lawrence) is Leland Stottlemeyer's ex-girlfriend and a real estate dealer. The two began dating shortly after she hired Monk to investigate damages to her car in "Mr. Monk, Private Eye," and she even sets Stottlemeyer up with a new apartment. The two continued to see one another, but their dates were often interrupted, postponed or cancelled as a result of Stottlemeyer's duties. She resorted to bidding on a date with him at a bachelor auction just to get him alone in "Mr. Monk and His Biggest Fan". The relationship ended after Monk proved her the murderer of her former partner in "Mr. Monk and the Bad Girlfriend," leaving Stottlemeyer to wonder if the relationship was real or merely something she'd planned from the beginning. At the end of the episode, he tosses something into the ocean, saying "It's only a rock," suggesting that he was going to propose to Linda while in Hawaii.

Harold J. Krenshaw (Tim Bagley) is another patient of Dr. Kroger who also suffers from Obsessive Compulsive Disorder. Despite sharing the same disorder, Harold and Adrian Monk are constantly at odds, mostly over which of them is liked better by Dr. Kroger. In addition to his OCD, Harold also suffers from acute paranoia and narcissism. As a result, he deludes himself that everyone is out to get him, either because of his importance in the scheme of things, or because he inspires outrageous jealousy in everyone else. He often takes great pleasure in "getting" other people before they get him, especially Monk.

Harold first appeared in "Mr. Monk and the Girl Who Cried Wolf" when he and Monk bicker over the arrangement of magazines in Dr. Kroger's waiting room.

In "Mr. Monk and the Election" Harold won (against Natalie Teeger) to become a member of Julie's school board.

In the episode "Mr. Monk Gets a New Shrink," Harold takes a bullet to save Dr. Kroger's life (much to Adrian Monk's dismay).

In "Mr. Monk and the Daredevil," Harold eclipses a jealous Monk in fame when the public at large believes him to be a notorious Human Fly known only as The Frisco Fly. In reality, Harold was dropped into the role by his cousin who was trying to kill him over an inheritance. Unaware of the murder plot, Harold went along with the charade because he loved the public attention, getting a golden opportunity to infuriate Monk, and gaining new respect and admiration from his son.

In "Mr. Monk and the Buried Treasure," Monk agrees to help Dr. Kroger's son Troy decipher what appears to be a treasure map in an attempt to once more out-do Harold, who has just given the gift of a wristwatch to their therapist.

In "Mr. Monk Gets Hypnotized," following the death of Dr. Kroger, Harold tries hypnotic regression therapy with a new doctor (played by Richard Schiff) which at first seems to cure him of his OCD, inspiring Adrian to try it as well. However, the therapy later backfires when Harold's feelings of euphoria lead him to take off all his clothes in public, and he is arrested for indecent exposure.

Harold made a brief cameo appearance in "Mr. Monk's 100th Case," as a talking head on a television special commemorating Monk's achievements as a detective, which Harold derided.

Harold's latest appearance is in the seventh season finale, "Mr. Monk Fights City Hall." Now serving on the San Francisco City Council, Harold gleefully votes against Monk's motion to preserve the parking garage where Trudy Monk was murdered, instead of demolishing it to build a children's playground. At first, Monk sways the a majority of the council to vote in his favor, but inadvertently tips the vote when he insults one of the other council members while exposing a murderer. Harold also (thanks to an inadvertent slip from Natalie) learns the name of Monk's new therapist, Dr. Bell, whom Adrian has been bragging about, and announces that he will also be seeing Dr. Bell in the future.

Harold is married and has a son, Jimmy.