Mycroft Holmes was the brother of Sherlock Holmes and an ally of Bernice Summerfield. (AUDIO: The Adventure of the Diogenes Damsel)
In 1882, Mycroft visited Sherlock to inform him their father, Siger Holmes, had died. He reminded Sherlock that, because of this, he had a duty to their sister, Genevieve Holmes. This was enough to persuade Sherlock to travel with him back to Yorkshire. (PROSE: Erasing Sherlock)
In 1911, he invited Sherlock to the Diogenes Club. He wanted his expertise to discover who was behind the explosion in bookshops. (AUDIO: The Adventure of the Bloomsbury Bomber)
The Seventh Doctor, Ace and Benny met Mycroft while he was in the employ of the British government. (PROSE: All-Consuming Fire)
In 1916, Mycroft was working for the British government during World War I. (PROSE: The Found World)
In 2010, Steven Moffat and Mark Gatiss created the BBC Wales series Sherlock, starring Benedict Cumberbatch as Sherlock. Steve Thompson is the third main writer of the series. In their version, Mycroft Holmes, played by Gatiss himself, is a major character, featuring in twelve of the thirteen episodes so far.
Mycroft has been played by Peter Jeffrey, Jerome Willis, Richard E. Grant, Derek Francis, Stephen Fry and John Sessions.