"I need a hero 'til the end of the night and he's gotta be strong and he's gotta be tuff" - thus defines ... a hero in her song "I need a hero." In addition to those features a traditional hero is also respected by the majority, ready to sacrifice him- or herself for the sake of the safety of a neighbor and is ultimately good. On the other hand, one can also understand the term "hero" as "protagonist", but this meaning of the word is hereby irrelevant, since due to uniqueness of every novel one can hardly formulate a typical main character.
However the first condition for the typical hero to come about is the typical setting. For example one needs clearly distinguished good and evil forces, a problem to solve etc. "Catch 22" is not a typical novel - there are no clearly distinguished opposite forces: everybody can be justified - Americans are emancipating the country, Germans enlightening and "setting world in order", Italians trying to found the means to survive.
Variety of small problems to solve and abundance of a clearly distinct major one, make this novel even more different from a typical one. Hence there is no space for a typical character - it is unable to fit in. However the relations between John Yossarian, the main character of the novel, and a typical notion of heroism is still present.
Devotion to the oppressed is an essential feature of a hero. Yossarian however betrays his squadron-mates and the innocent people. He agrees to fly Milo Minderbinder on his trade trips (chapter 22, page 263) and thus makes his impact into the growing of the M&M Syndicate. The organization established by Milo Minderbinder was controlling a big part of world's black and legal markets. Due to...