Along with his partner Luther Banks, Harold Simmons began his career in the United States Marines until he was discharged with cause. In the aftermath of the Battle of New York, Harold worked for an elite anti-alien task force known as the Advanced Threat Containment Unit, in which he and Banks worked with Rosalind Price.
Following the Inhuman Outbreak, Harold Simmons served in Banks' unit in tracking down and capturing any Inhumans who appeared as a danger to the citizens. One of these incidents involved Joey Gutierrez, a man who gained the ability of melting metal. Harold was with Banks when he and the whole unit attend to capture Gutierrez, who begged for assistance as he claimed to have no idea what was happening to him, but when he accidentally used his powers to melt the team's guns, Harold was given the order by Banks to shoot him down, but was unsuccessful when Gutierrez was able to cause a car to explode and ran away in the chaos.
Joining the Watchdogs
After Banks' death, Harold Simmons left the ATCU and joined the Watchdogs in tracking down and killing Inhumans rather than sparing them. He and his team were this close in targeting and killing an Inhuman named Bryan Cole, but was defeated by a team of S.H.I.E.L.D. agents and handed over to Brigadier General Glenn Talbot.
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