Ambrose Monk is the older brother of Adrian Monk.
Ambrose, like his brother Adrian, possesses uncanny powers of deduction and memory. Unfortunately, he suffers from a severe form of agoraphobia. As of 2003, he had not left the home he grew up in since 1971.
- Ambrose Monk is apparently a homage to Mycroft Holmes, the older brother of Sir Arthur Conan Doyle's famous detective Sherlock Holmes. Mycroft was also written as being more intelligent and better at deduction than his younger brother, but lacked any ambition or energy to follow through with his theories, thus rendering him useless as a "true" detective.
- While only speculation, it is possible that Ambrose cared for the boys' mother at home, as Adrian comments more than once she was sick for a very long time but did not pass away until 1994.
- Ambrose continues to live in the house where he and Adrian were raised. He keeps all incoming mail addressed to their father, who left them when they were young, and he also keeps copies of the daily newspaper. He expects their father to return at any time and want to see these items. Ambrose also keeps his father's study as it appeared on the day the father left the family.