Nothing is knew about Colossal Craig's backstory, but it is assumed that he was at one point arrested for some crimes (perhaps manslaughter or vandalism) and jailed for that.
"Colossal" Craig started out as an inmate who successfully broke out of jail. His escape made it to the papers, and Captain America was after him. Craig planned then to take children hostages in order to remain free.
The next afternoon Craig crashed into a street lamp with his car in front of an elementary school. He took two boys as hostages and carried them back into their school while threatening them with a gun and telling Cap to back off. Inside the empty school Craig hid with the boys in a classroom and shot through a window when he saw Cap's colors, but it was only a flag.
Cap broke through the other window, disarmed Craig with his shield and attacked him. Craig struck back and tried to smash Cap with the teacher's desk. Cap was able to avoid the attack, but Craig tried the same with a chair. This time Cap used a duster to blind Craig.
A few hard hits to the body failed, and Craig used a bearhug against Cap who freed himself with a clap of the ears. Cap started his comeback with a fire extinguisher to further cool down Craig, but the colossal one headed for his gun. Cap reached the gun earlier and tossed it away. Cap then used kicks and punches to knock out Craig for good.
After this, Craig was presumably put in jails again for everything he did, and were never heard again.
Colossal Craig is a tall caucasian male in his late thirties/fourties, albeit his exact height and weight are unknown. He has blond hairs. His casual outfit consists of a white shirt, and cyan jeans and boots.
A fierce brute, Colossal Craig wasn't afraid of everything, except one thing: to be jailed again for his crimes. As such, he is willing to do everything in order to avoid jails. He is extremely violent, ruthless, destructive and egotistic, as he doesn't care about anyone except himself. In addition, he has very little standards, as he has no qualms to take children hostages.