Source: dc.wikia.com
3. Congo Bill
The man who would be Congorilla started off as simple Congo Bill, who was a ‘30s and ‘40s DC adventure hero.
“Congo Bill†is also the name I’d take if I ever managed to get hired as a Jungle Cruise tour guide, if you were interested.
But one day Bill tried to save a strange old witch doctor. He failed, and the witch doctor died. But before he died, he gave Bill a strange ring that allowed Bill to switch his mind into a giant golden ape called Congorilla. What happens to Congorilla’s mind isn’t mentioned, but who cares, he’s a gorilla and his life doesn’t matter as much as a human’s. What’s great about that last sentence is you can read it as either sarcastic or fully serious, depending on your own personal views, and it reads fine either way. Not telling you which way I meant it as, that’s just gonna be one of those mysteries of life.
Like how exactly Congo Bill got on the Justice League because THAT HAPPENED.

