Despite a careless streak that once caused the laboratory he was working in to explode, he became a close friend of Tony and was soon appointed head of Stark Industries' research department.
Tony then decided to reveal to Kevin his secret identity of Iron Man, and to build for him a second suit of armor for use in the event of an emergency.
That emergency would come a short time later, when Iron Man and girlfriend Marianne Rodgers were taken captive by the superhuman madman Mikas the Soulfather.
In an attempt to stop him without hurting him, Iron Man's repulsor rays were trained on the vehicle and accidentally hit its fuel supply.
Some months after Kevin's death, when the details of the incident came to public light, Michael, a sergeant in the New York City Police Department, decided that the official investigation exonerating Iron Man's actions was a cover-up.
[6] O'Brien finally hired Harry Key, an unscrupulous private investigator, to get him inside the Long Island plant.
Escaping his confinement, O'Brien decided that he was wrong about Stark and determined to help him by donning the now-cooled Iron Man armor.
[7] After Iron Man defeated the Mandarin, Stark fixed the malfunction in the Guardsman armor's circuitry so it was safe to wear.
The Guardsman armor contained a powered exoskeleton that gave the wearer superhuman strength, allowing the operator to lift 40 tons under optimal conditions for about 3 minutes.
The Guardsman armor can fly via chemically-powered boot jets at a maximum speed of 250 mph (400 km/h) for three hours, and contains 30 minutes air supply for submersion or high-altitude flight.
Each palm of the Guardsman armor's gauntlets contains a charged ion "repulsor ray" emitter, capable of 45 seconds of continuous discharge at a range of 40 feet (12 m) before irregularities in the plasma cone diffuse the beam.
Both Kevin and Michael suffered from emotional instability that was exacerbated by the cybernetic circuitry in the original Guardsman battle-suit, causing both men to go insane.
Although superior to the Stane models, the new Stark Enterprises suits were limited to operation within the vicinity of the Vault, as a security measure to prevent misuse of their Iron Man-derived technology.