Steranko paintings graced the covers of this Shadow massmarket paperback series that ran for 23 volumes between 1974 and 1978.

From the back cover:

WHO KNOWS WHAT EVIL LURKS IN THE HEARTS OF MEN?

"I have just freed myself from the power of a fiend!” whispered Worth Varden. “A fiend who would stop at nothing. A super criminal whose schemes are but, in the making,...."

Hours later, Varden was dead. And with him went all he knew about the worldwide dope dealing and blackmail empire of the all-powerful crime baron known only as...Gray Fist.

Gray Fist--so treacherous that he found no act too vile, no lie too base to inflate his ill-gotten wealth. Gray Fist--so secretive that even his closest henchmen could not guess his secret identity. Gray Fist--so diabolically cunning that his climb to power seemed unstoppable.

Was there anywhere a crime fighter so agile of brain and hand that he could match wits with this infamous lord of the underworld! There was--lurking in the darkness, laughing a soft eerie laugh, stealing into the innermost sanctuaries of the forces of evil, facing singlehanded the guns of mobsters by the dozen... The Shadow!