The most famous of Captain Americas part-time demises was his first. Steve Rogers first appeared in the pre-Marvel era, a character whose debut saw him punching Hitler square in the jaw a good few months before the US had even entered the war. His adventures actually continued past 1945, with the Star-Spangled Man moving onto Commies instead of Nazis. Of course, eventually Cap fell out of favour during the mid-fifties (when superheroes reached an all-time low in popularity and would mostly supplanted by sci-fi and horror books), and wasnt killed off but his title did get cancelled. It wasnt until a decade later Stan Lee thought to bring him back in the pages of Avengers #4, 1964. Its there that Lee also retconned Captain America's history so that Cap didnt fight past World War II, and was in fact missing, presumed dead after a botched attack on Hydra villain Baron Zemo saw him and teen sidekick Bucky aboard a drone plane full of explosives headed for the US. They knocked it off course, but supposedly died in the crash.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/