I'm sure you've seen some of his work. Among many other things, he was simply the most awesome printmaker ever. ;) The man did things in woodcut that most guys couldn't even achieve in engraving, and his engravings ruined engraving as an art medium for everybody else, forever. After him, artists decided that they'd better explore new print media like etching instead of trying to compete.

It takes a lot of awesome to kill a whole art medium.

I've also heard him described as the man that brought the Renaissance to Germany.