Winston Churchill in 1938 - He condemned Chamberlain's Munich peace of our time and urged war to be declared on Germany.
Not that Churchill ever "urged war to be declared on Germany", but appeasement was a controversial policy which had many opponents both in the Conservative and opposition Labour party (which was opposing appeasement by Munich). Churchill was viewed as a crank in 1938 because he had spent the 20s and 30s burning bridges with everyone he could and generally acting like an incompetent buffoon, e.g. being the worst Chancellor of the Exchequer in history, advocating the murder of Gandhi and attempting a bizarre stunt during the Abdication Crisis where he tried to break the government by supporting the King.