George Carlin, 1937-2008. Carlin was one of my first exposures to stand-up comedy. He was one of my dad's favorites, and he became one of mine. He's famous for his shockingly offensive routines - but unlike too many other "shock humorists," Carlin was side-splittingly funny and, once you realized there was a purpose behind all the naughty words, rather cerebral.
For kicks, here's his famous "Seven Words You Can't Say On Television" routine. Or one of my favorites, on sports. And for those of you who like your comedy clean, enjoy the Hippy Dippy Weatherman.