Dr. Charles Kroger was Mr. Monk's beloved psychiatrist. Perhaps the most tolerant of all of Adrian Monk's friends, Kroger is a psychiatrist who serves as the closest thing to a rock for Monk. While he does engage in talk therapy, he does not prescribe an SSRI medication, which is commonly used by psychiatrists to treat OCD, because when he did, in the episode "Mr. Monk Takes His Medicine", Monk lost his ability to solve crimes. Kroger is instrumental in trying to get Monk reinstated as a detective, while discussing his problems and progress as a person. Most of Kroger's scenes help move Monk's character forward. Similarly, Dr. Kroger has also (usually unintentionally) helped Monk solve several cases. In "Mr. Monk Gets a New Shrink" he temporarily quit after his maid was murdered, since the police thought that one of his patients was responsible. It later turned out that it was actually one of his co-workers, Francis Merrigan, who was responsible, in order to cover his tracks as he was secretly a Heroin smuggler (the maid accidentally smashed one of the Turkish figurines containing the Cocaine samples, and after stealing back the Cocaine from the vacuum cleaner, he killed the maid), although not without being held hostage alongside Monk after they solved the case.
Kroger is also the subject of an ongoing feud between Monk and Harold Krenshaw, another patient with similar problems. While very forgiving, even Kroger gets fed up with Monk from time to time, most heavily demonstrated in one episode (Mr. Monk and the Sleeping Suspect) where Kroger came back from vacation and saw Monk standing outside his home. Kroger simply instructed the cab driver to just keep driving and kept his head low to avoid Monk. On another occasion in Mr. Monk and the Garbage Strike, when the city stopped collecting garbage, Monk sent his garbage to Dr. Kroger's house. When questioned about it, Monk denied it before Kroger told him it was specifically sorted, boxed, and written in his handwriting.
On the other hand, there have also been several cases in which Dr. Kroger has been the only person capable of getting through to Monk during difficult situations, such as when Monk was brainwashed by a duplicitous cult leader played by Howie Mandel (Mr. Monk Joins a Cult).
It was revealed in the 15th episode of Season 3 ("Mr. Monk and the Election"), that Kroger is married and has children (a son), and is also Jewish, although his wife was apparently Irish Catholic. In the first episode of Season 5 ("Mr. Monk and the Actor"), Monk felt he needed take up the entire week with therapy sessions after a particularly traumatic situation where he had to deal with the Monk actor acting like him and nearly causing a suspect to be killed in blind rage for the murder of Trudy as part of a misunderstanding. Kroger says he does not like working on the weekends so he can spend time with his wife and kids. In the episode "Mr. Monk Gets a New Shrink", it is revealed that he has a wife, Madeline, and a rebellious adolescent son, Troy, who denies that he is their child.
Kroger has a stormy relationship with his son, and was forced to take a paternity test three times at the "request" of his son. Troy calls his parents by their first names and knows Lt. Randy Disher from possibly being arrested. Disher asked if Troy had kept out of trouble, to which Troy said "no". Troy later appears in the Season 6 episode "Mr. Monk and the Buried Treasure". In this episode, while skateboarding with two friends, he finds a map leading to what he assumes is money. He and his friends ask Monk to help them, saying it is a school project. Monk agrees to help them, and they eventually find it. Monk, however, later discovers he's been tricked and tells Troy to come with him back to where the buried treasure was, leading to them temporarily being trapped in Troy's car. By the end of the episode, Troy has a better relationship with his father.
Dr. Kroger may not have been a strong paragon for honesty, as, according to Troy when explaining how they found at most $5,000 under the red x instead of the $2 million that the bank robbers managed to steal and allegedly buried, Dr. Kroger lied to the police about having a rare coin collection in order to "rip off the insurance company."
In the Season 7 premiere episode "Mr. Monk Buys a House", it was revealed that Dr. Kroger has died of a heart attack, five weeks before the episode took place. (This was because actor Stanley Kamel died of a heart attack.)