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 his brother Sherlock to inform him that their father had died. He reminded Sherlock that he had a duty to their sister, Genevieve, and persuaded Sherlock to travel with him back to Yorkshire. (PROSE: Erasing Sherlock)
In 1887, Mycroft met the Doctor while in the employ of the British government. (PROSE: All-Consuming Fire)
In 1893, Mycroft and Bernice Summerfield investigated a series of crimes perpetrated by a group of Cwejen who were attempting to ritually summon their "Pale God" — a memory of the Doctor. (AUDIO: The Adventure of the Diogenes Damsel)
In 1911, he invited Sherlock to the Diogenes Club. He wanted his expertise to discover who was behind a series of explosions in bookshops. (AUDIO: The Adventure of the Bloomsbury Bomber)
In 1916, Mycroft was working for the British government during World War I. (PROSE: The Found World)