You know all those things you like about America? The huge tracks of untamed land, the cities bustling as one of the mothers of western industry, the pioneer culture that eventually tamed The Wild West? The music of Aaron Copland (1900-1990) is basically all that distilled into the purest musical form you could imagine. Go listen to "Fanfare for the Common Man". Now.
Aside from that well-known piece, Copland is most famous for his ballet music for Billy the Kid, Appalachian Spring, and Rodeo (especially the "Hoedown" movement from the latter, which you've almost certainly heard, either in a Western or in the background while someone told you what beef is for.)
Copland also composed music for a few movies, including Of Mice and Men (1939), Our Town (1940), The Red Pony (1949) and The Heiress (1949; Academy Award winner for Best Music, Scoring of a Dramatic or Comedy Picture).
Copland actually began making music that attempted to emulate the foremost German composers of his time, until his teacher told him that he was trying to hard and that he should simply be himself (i.e. an American). And it worked.
Because of Copland's Americana styles, right-wing politicians frequently use his music or a Suspiciously Similar Song version of his music in their campaign ads. Ironically, Copland was quite openly gay and left-wing with Communist views. Joe McCarthy didn't like him very much.
Hugely influenced by early modernist musicians, like Stravinsky and Debussy, Copland in turn influenced such Hollywood composers as Elmer Bernstein (whose theme for The Magnificent Seven in particular is sometimes mistakenly credited to Copland).