Origin

Little is known about Mycroft's early life. He was born seven years before his younger brother, Sherlock Holmes. They were descended from country squires, and almost certainly raised wealthy. He most likely attended university before obtaining a position with the British government. Though he describes this position as "minor," he actually holds a very important, if nebulous office, acting as a sort of human database for all government affairs. At some point he co-founded the Diogenes Club. 

Creation

Mycroft was created by Sir Arthur Conan Doyle. He made his first appearance in "The Adventure of the Greek Interpreter".  

Major Story Arcs

Sherlock Holmes

Mycroft appears as Sherlock's elder brother, a powerful government official who occasionally brings his influence to bear on behalf of his brother. He also occasionally offers aid in the form of his inductive abilities, but his dislike of legwork leaves his brother to acquire the evidence. 

The League of Extraordinary Gentlemen 

Following the death of Professor Moriarty, Mycroft assumes the role of head of British intelligence, also using the name "M". In this role, he has command over the League, sending them to investigate the Martians and Mack the Knife, among other missions. 

Powers and Abilities 

Mycroft is extremely intelligent, possessing inductive abilities greater even than his famous brother. His intelligence is offset by his indolence and disinclination to collect or provide evidence for his conclusions. He also possesses an excellent memory, as he is able to retain vast amounts of information pertaining to his position in the government. 

Other Media

Film

The Bruce-Partington Plans  
Mycroft appears in this film adaptation of the story of the same name. He is played by Lewis Gilbert.  
A Study in Terror  
Mycroft appears in this film, which centres on Sherlock's hunt for Jack the Ripper. He is played by Robert Morley. 
The Private Life of Sherlock Holmes   
Depicted quite differently from how he appears in the original stories, Mycroft appears in this film as the probable head of the secret service. He is played by Christopher Lee. 
The Seven-Per-Cent Solution 
Mycroft appears in this film adaptation of the book of the same name. He is played by Charles Gray.  
Sherlock Holmes: A Game of Shadows
Mycroft appears as the somewhat mysterious, if still jovial, elder brother of Sherlock Holmes. He is played by Stephen Fry. 

Literature

Sherlock Holmes Canon 
Mycroft was originally created for the Sherlock Holmes series of stories. He appears in three stories and is mentioned in a further one. 
Enter the Lion: A Posthumous Memoir of Mycroft Holmes 
Mycroft is the protagonist, a minor Foreign Office official, in this novel by Michael P Hodel and Sean M Wright.  
The Mycroft Memoranda 
Mycroft makes a minor appearance in this book by Ray Walsh. 
Anno Dracula  
Mycroft appears as a vampire in this novel by Kim Newman.  
All-Consuming Fire 
Mycroft appears in this pastiche the Holmes stories, HP Lovecraft's Cthulhu Mythos and Doctor Who by Andy Lane. 
Mary Russell Series 
Mycroft appears in this series of books by Laurie R King. He makes his first appearance in the second book in the series, A Monstrous Regiment of Women. 
Mycroft Holmes Series  
Mycroft is the protagonist in this series of detective novels by Quinn Fawcett. There are four books in the series. 
Thursday Next Series 
Author Jasper Fforde reveals Mycroft to be the protagonist's uncle, who travelled into the Holmes stories and became Sherlock's brother. He makes his first appearance in The Eyre Affair. 
The Italian Secretary  
Mycroft appears in his traditional role of government official in this novel by Caleb Carr.  
Enola Holmes Series 
Mycroft appears as the much elder brother and disapproving guardian of the main character, Enola.  
Young Sherlock Holmes  
Mycroft features in these books based on the young Sherlock's adventures written by Andy Lane. 

Television  

Sherlock Holmes  
Mycroft appears in one episode of this German television series, "Die Bruce-Partington-Pläne". He is played by Hans Cossy. 
Sherlock Holmes 
Mycroft appears in two episodes in this series, "The Bruce-Partington Plans" and "The Greek Interpreter". He is played in the first by Derek Francis, and in the second by Ronald Adam. 
The Adventures of Sherlock Holmes and Dr Watson 
Mycroft appears in four of these Russian made-for-television films. He is played by Boris Klyuev.  
The Adventures of Sherlock Holmes
Between this series and its continuation The Return of Sherlock Holmes, Mycroft appears in two episodes. He is played by Charles Gray.  
Alfred Hitchcock Presents  
Mycroft appears in the episode "My Dear Watson". He is played by Graeme Campbell.  
Hands of a Murderer  
Mycroft appears in this made-for-television film. He is played by Peter Jeffrey.
Sherlock Holmes and the Leading Lady
Mycroft appears in this made-for-television film. He is played by Jerome Willis. 
Incident at Victoria Falls 
Jerome Willis reprises his role in this made-for-television movie.  
The Memoirs of Sherlock Holmes  
Replacing Dr Watson in one and Sherlock in the other, Mycroft appears in two episodes, "The Golden Pince-Nez" and "The Mazarin Stone". He is played by Charles Gray.  
The Royal Scandal 
Mycroft appears in this made-for-television film. He is played by RH Thomson.
Sherlock: Case of Evil 
A semi-crippled Mycroft, so injured by an encounter with Moriarty, appears in this made-for-television film. He is played by Richard E Grant. 
Sherlock
Mycroft appears as a shadowy government official who appears to control most of the intelligence operations for his government, and possibly those of others as well. He is played by Mark Gatiss.   

Radio

Sherlock Holmes  
Mycroft appears in the 1950s BBC radio adaptations of some Sherlock Holmes stories. He is voiced by Val Gielgud.  
Sherlock Holmes  
Mycroft appears in three episodes of the 1990s BBC radio adaptations of some Sherlock Holmes stories. He is voiced by John Hartley. 

Video Games 

Sherlock: The Riddle of the Crown Jewels   
Mycroft appears in a minor role in this game. 
The Lost Files of Sherlock Holmes: The Case of the Rose Tattoo  
Mycroft has a featuring role in this PC game.
Sherlock Holmes vs. Jack the Ripper 
Mycroft appears briefly to offer assistance to Sherlock.