Batman villain best portrayed by
Frank Gorshin in the
'60s TV series. Wore green tights with question marks all over. Also extremely
hyper, often
jumping around while doing his
rapid-fire laugh.
Played to a lesser extent by Jim Carrey in one of those crappy movies.
More important, the Riddler was part of Bob Kane's original Batman comics (first appearance: Detective Comics #140, 1948). His M.O. was to leave riddles, cryptograms and other puzzles hinting at his next crime scene, being mentally incapable of committing crimes without leaving clues behind. Unfortunately for him, Batman always had the intelligence to decipher the clues.
His real name was Edward Nigma ("Nygma" in the Batman movie), and while the movie and animated batman series paint him as being driven over the edge to a life of crime, the original character was driven by ego, not insanity. (See Edward Nigma.)
"The Riddler" is also some kinda Web site that ran contests, found at riddler.com (see Riddler).