He is a member of the British secret service, though his exact job is unknown. He has a habit of picking John up to get him to take on cases for Sherlock or just to check on the well-being of his little brother.
He often carries around an umbrella, the reason for this is unknown.
Mycroft first appears when he abducts Watson to offer him money for reports on Sherlock, an offer that John refuses. He is also able to tell from John that he has a theripist, and that he enjoys danger, which is why the tremor in his hand has stopped. When John asks who he is, he tells him that Sherlock would consider him as his Arch-Enemy, causing some confusion.
Mycroft is later revealed by Sherlock to be his older brother. The two don't get on well, Sherlock especially despises his older brother, the exact reasons are unknown.
He often tries to enlist Sherlock's help when a case he's given requires "leg-work". Sherlock often refuses, even if he still investigates in secret what Mycroft has asked him to.
Despite Moriarty's nickname for him "The Ice Man", Mycroft does truly seem to care about his brother. He phones John ahead, to warn him that it might be a bad night for Sherlock after Irene Addler's supposed death, and insists John stays with him. He is also willing to pay Irene off rather than reveal Sherlock as a security leak.
He and Sherlock still behave like squabling children occationally, most notably in the first episode of the second series, when they start arguing in Buckingham Palice; John ends up having to intervine.
Sherlock steals Mycroft's security cards to get into areas such as Baskerville. It takes Mycroft about half an hour after its use to realise what Sherlock has done. In the same episode Mycroft sends Lestrade down to Devon to keep an eye on him and John.
In the last episode of the second series, Mycroft plays a large part in Sherlock's downfall. He tells Moriarty (then a prisoner) all about Sherlock's childhood, allowing Moriarty to exploit that information to portray Sherlock as a fake.
When John blames Mycroft for Sherlock's death, Mycroft does seem guilty and distressed by his brother's death. It is unknown whether at this point he knows that his brother did not die.
There are many suggestions that Mycroft is just as intellegent as Sherlock, he's just lazier.
- He is a member of the secret service
- He always carries an umbrella
- He never texts if he can talk