Simon Marshall was an ex-pharmaceutical chemist who was working for the Maggia to develop a new designer drug to act as a cheap substitute for imported heroin.

Marshall would lure in runaways and homeless people to his lab on Ellis Island by having his men offer them food and shelter, only to instead simply test his new drug on them. This is how teenage runaways Tandy Bowen and Tyrone Johnson were brought into Marshall's clutches.

Tandy and Tyrone were brought to Marshall, who injected them with his latest drug, D-Lite, which had up till now proven fatal to others. The two runaways ended up surviving the ordeal however, and Tyrone and Tandy were unintentionally empowered to become Cloak and Dagger.

He was killed by Dagger who she searched her vengeance for killing other kids.