Since the Riddler usually rates among the favorite Batman villains on other threads here at CBR, and it looks like he's going to be around in the current Catwoman comic book for now, I thought it might be a good idea to give him a fresh thread all his own.
Cover to his first appearance in Detective Comics #140 (October 1948):
From Who's Who: The Definitive Directory of the DC Universe Vol. XIX (September 1986),
And the cover of last month's Catwoman #29:
though I have no idea why his question marks are backwards . . .