Whenever you put Sherlock Holmes on screen it will always, inevitably, be wrong (too many changes, not enough changes, wears a deerstalker, is too gay, not gay enough… etc) but on the whole, people are quite forgiving of Sherlock. We’ll accept a short, blond Holmes as long as you get Watson right. People are less forgiving of a bad-Watson.
But what about Mycroft?
I did a quick search for Mycroft on the IMDb character search and you’d be surprised looking at the list of some of the actors who have portrayed him:
Only Fry & Gray (with apologies, neither can be described as ‘corpulent’) come even close to the description of our first encounter with the elder Holmes: “Heavily built and massive, there was a suggestion of uncouth physical inertia in the figure.” (GREE). Holmesians get upset when writers ‘mess around’ with Sherlock and Watson but Mycroft is fair game.
In the truly awful ‘Case of Evil’, Richard E Grant plays a crippled former drug-addicted version of Mycroft. It’s one of those reveals that makes a terrible film just that little bit worse. Christopher Lee plays closer to canon, you can believe “he is, on occasion, the British government.” even if he physically doesn’t resemble the character. Stephen Fry is a buffoonishly bizarre Mycroft but it’s a clever piece of casting and Boris Klyvuev’s Mycroft has perhaps the greatest developed home life of any (so far) – he’s very fond of his dog (a red setter), has a son and works for the Foreign Office. There’s no reason why Mycroft can’t have a son, unless you take Sherlock’s comments about “no ambition and no energy” very literally.
Out of all the Mycroft’s, I would argue that Mark Gatiss is the truest version will ever seen on screen. A dangerously clever man who runs the British government and has an ongoing weight problem.