Alias: Patient 29

Tremor is a former employee of the mob boss Antonio Twistelli who "volunteered" for the mob's efforts to make the ultimate hitman. Tremor (whose real name is Richard Masullo) only agreed to the program after the mob threatened the lives of his family members.

At some point Masullo was handed over to Jim Downing (pre-coma) and in turn handed over to Carlos Nortego for experimental genetic testing. Unfortunately, the experiment went horribly wrong and Richard was transformed into a huge, bio-mechanical monster. To cover their involvement, the mob killed Richard's family anyway, including his beloved Anna-Marie.

Destroyed both emotionally and physically, Tremor began living in the alleyways plotting his revenge on Twistelli. After Spawn's presence in the alleys drew the personal attention of Twistelli, Tremor took notice as well and orchestrated a meeting with Spawn himself.

After listening to Tremor's tale, Spawn gave him a top secret file on Twistelli's activities out of pity. Tremor left, not sure if Spawn was a friend or foe, but thankful for the file he received.

Later, Tremor returned to Spawn to get his help storming Twistelli's offices. Tremor had discovered Twistelli had been gathering information on Terry Fitzgerald and his family, and he knew that this info would convince Spawn to help.

When they attacked Twistelli's office, however, their shaky partnership collapsed. Tremor discovered that his brother David was working for Twistelli, and he was barely able to save him from Spawn's wrath. Amidst the fight, Tremor quickly scrambled away to find medical care for his brother David.
 
Years later, Richard Masullo (in human form) watched intently as Jim Downing began to receive media attention on TV. He set off to New York from the midwest, presumably to find the new hellspawn.