Older brother of Sherlock Holmes, and his equal or better in mental power. However, Mycroft is extremely lazy and won't go outside of his home, work or club, even to research a case, so he calls in Sherlock when he wants legwork done, and Sherlock comes to him for government-related information because of Mycroft's job.

Also a self-aware computer in Robert A. Heinlein's The Moon Is A Harsh Mistress, who named himself after Holmes' brother, but is usually called Mike.