Alan Turing: Why was the codebreaker convicted and pardoned for his sexuality?

Who is Alan Turing and why is he on the new £50 note?""HeartFifty pound note: Alan Turing, World War 2 codebreaker, to feature on new note""ExpressAlan Turing is new face of £50 bank note - first gay man to get honour""Mirror OnlineSecond World War code