Fabian attacked the Avengers on more than one occasion as a means of gaining prominence and attention. He was always quickly dispatched by the team. On one occasion he attacked the home of the Wasp when she had invited a group of female heroes over with the aim of inviting them to join the Avengers. Some of the women left during the attack, feeling he wasn't worth bothering with, and he was swiftly defeated by the Wasp and the She-Hulk.

Fabian later applied for Avengers membership as Mechanaut alongside Gladiatrix, Blue Shield, and Speedball. While he was putting them through their paces, Captain America had to leave the applicants alone. While they were on their own, the quartet were surprised by the sudden appearance of the Soviet Super-Soldiers, who were trying to defect from the Soviet Union. Thinking the Soviets were part of their test, the four applicants attacked them, but were none too successful against their more experienced opponents, with Fabian accidentally getting in the way of his own temporary teammates. Captain America returned and stopped the fight, and rejected the four of them, saying they weren't ready for Avengers membership.

Eventually Captain America hired Fabian as an staff member and inventor on the Avengers' expanded ground crew to turn him from his life of crime. Fabian was enthusiastic, but often felt overshadowed by some of his SHIELD and military-trained colleagues. When the Avengers' then headquarters, Hydrobase was attacked by robots sent by Doctor Doom, Fabian donned his battlesuit to help the rest of the support staff defend the base. Fabian was almost harmed, however, when he underestimated the robots' ability to survive damage. The base was sunk, but the staff, including Fabian, escaped.

Although Fabian successfully assisted Captain America on more than one adventure, he has fallen victim to numerous personal demons. For example he became addicted to the drug "Ice" and has had sucidal tendencies at times. Fabian often creates items that are maladroit or out of control. Through his struggles, Captain America (Steve Rogers) has remained a loyal friend to Fabian. When the Avengers asked Fabian to leave the Mansion, Cap moved out of the mansion and in with Fabian in Brooklyn Heights.

When Captain America and the Avengers were believed to be killed during Heroes Reborn, Fabian constructed robot versions of the Avengers to protect the city. These robots also had some malfunctions. When the Avengers returned, they discovered Fabian was behind this scheme and disarmed him. Fabian was in a state of exhaustion and derangement from months of constantly operating the robots without any outside assistance.