Abel is actually nothing more than a genetically engineered replacement body created for use by M. Bison. He was to be disposed of with the other failed specimens, but he alone managed to survive and escape.
After being saved from a burning lab by the commander of a mercenary group, Abel woke severely injured and with a case of amnesia.
The commander looked after the young Frenchman and became a father-like figure.
Before the commander's passing, he told Abel that the lab he was found in was actually the former base for Shadaloo and he should be wary of the crime organization.
Now out on his own with his amnesia still haunting him, Abel works with Chun Li to investigate the rumors surrounding the presumably destroyed Shadaloo syndicate, using his mixed martial arts combat to enter the new fighting tournament.
How are you people so sure that he saw Charlie use the Sonic Boom that Abel saw? he probably saw it from seth who imitates other characters moves (Guile) and stop saying he is Charlie. Right now all we know is hes was suppose to be what seth is but he failed so he was thrown and rescued by some unknown man. And in his win quote against Seth he states "Why do you look like me? Am I even human?!" which may lead to the conclusion of: He isn't CHARLIE. My opinion shut up about it