Bruce Wayng is a man who was born in 1900, raised by bats, and disappeared in 1945 (all of which fits the time scale of Bat Mang, making him the most likely candidate for Bat Mang's real identity).
Little is known about what Bruce Wayng looked like, except that he looked a lot like Bat Mang.
From birth, Bruce was raised by bats due to the Bat Hospital Takeover of 1900. He attended school as a normal child would and thought nothing of his being raised by bats until he was 16, when he brought home his first girlfriend.
When Bruce Wayng's girlfriend saw he was raised by a pack of bats, she immediately fled and never spoke to Bruce again. This cause Bruce to re-think his outlook on life.
When Bruce turned 25, he gained control of his own company and left his bat family. He tried to never mention the fact he was raised by bats and eventually made his own family and became the CEO of Brucenomics Inc., his self-made business.
When Bruce turned 39, he began his mid-life crisis and was seen less and less until he disappeared completely in 1945.
Bruce Wayng probably is Bat Mang