When The Shadow debuted in pulp magazines in 1931, he was aviator Kent Allard, and he blackmailed Lamont Cranston into allowing Kent to assume his legal identity. When the radio series debuted in 1937, The Shadow was Lamont Cranston with no separate original identity.
Since the OP indicated in comments that this was what he had in mind, I'm giving it as an actual answer. Possibly the Silver Age Flash (Barry Allen)who premiered in Showcase #4 (October 1956). The "original" Flash was the "Golden Age" Flash (Jay Garrick).