Clinton McIntyre was always a violent person. But as he grew up, he realized that there's only one place where you can kill people and be honored for it and allowed to do it-the U.S Army. He joined the Army, but kept his hot temper and eventually killed his commanding officer. Right about this time, the U.S Army was working on a serum that would be the Super-Soldier Serum, and looking for a soldier to test it on. General Saunders was looking for a test subject, so he offered McIntyre leniency if he'd be the test. Someone else picked Steve Rogers as the official test subject, but Saunders disagreed, so he gave McIntyre the serum the night before Rogers. When he drank the serum, McIntyre got the power of the serum, but he went crazy with pain. He escaped and went on a rampage. He smashed up the lab, plus went out to the street and nearly killed a motorist before dying of a heart attack. His body was cryogenically frozen by SHIELD. 

Later, after the war, Agent Clete Billups found the frozen body. Billups was secretly an agent for A.I.M, and he stole the body and brought it back to AIM. AIM revived him and corrected the problems in the serum. They wanted Captain America dead, so they convinced him Steve Rogers was responsible for his death and that he'd stolen the mantle of Captain America. They gave him equipment like a reverse Captain America, named him Protocide, and set him loose to go kill Captain America.

Protocide looked for Captain America everywhere until he found someone that looked like Cap and was an ally of Cap. Protocide attacked him, although the man was a superb fighter and fought nearly evenly. The man was John Walker, the U.S.Agent, who had taken that name and become Cap's ally after their clash. Protocide severely injured U.S Agent but kept looking for Cap. He found Rogers and ambushed him. Since he had the element of surprise, he was able to badly injure Captain America. But before he killed him, A.I.M forced him to pull back. He went after him again and fought evenly with him. They fought to a draw, but Protocide slipped and fell into an energy reactor. Being a good man, Cap helped him out and saved him, but Protocide knocked him in and escaped. While running, he found that Captain America didn't seem to be as evil as A.I.M told him.

They fought their final battle when Cap, working with SHIELD, invaded the base he was in. They fought a showdown, but Protocide realized that Captain America had nothing to do with his past. When the A.I.M base exploded, Protocide hurled Cap out, escaping in the back of a pickup truck.