The Spook was a Batman villain from the early 70's who didn't make much of a splash afterwards, but I've always thought he made for some outstanding covers by the likes of Mike Kaluta, Dick Giordano, Nick Cardy, and Ernie "Chua" Chan.
The Spook, created by veteran artist and writer Frank Robbins, always put in mind of a Scooby-Doo villain, a seemingly supernatural menace who ultimately is revealed to be a mere conniving human motivated by simple greed or petty vengeance. In this case, Val Kaliban is a corrupt and murderous architect who uses specially installed secret passages to free convicts from prison for money.
Check out the Who's Who page and the splash page below illustrated by the painfully underrated Irv Novick.
Now enjoy this quite excellent cover gallery. The Spook wasn't featured on many covers, but they were all well above average.