Jeff Sullivan is the modern-day descendant of a mutant family that has latent superhuman powers, and traces its ancestry back to Gallix of Avalon. In 46 BC, Gallix' genes were altered by the god-like Fomore Levan. Since then, those among his descendents who are worthy of the "Soul of Levan" (hence the family name) are able to control their bodies' molecular structure, enabling them to fly, and endowing them with superhuman strength and relative invulnerability. The use of this power requires much energy, so it can only be sustained for limited periods of time. Jeff was later able to extend this by learning how to use ambiant cosmic energy. In the event of lethal blows, the Sullivans are able to transfer their consciousness into the bodies of their "twins" on parallel Earths.
Jeff Sullivan was born in Denver, CO. He discovered his powers ar age 24 when, after a potentially fatal electric shock, he found himself inside the body of his "twin" on a parallel Earth where Japan had won World War II and was occupying the U.S.A. After helping the resistance led by his cousin Patrick, Jeff was trained by the Council of Sullivans, comprised of his ancestors Maureen and Lagrid, and Adila and Korgath from the future. Having learned to master his powers, Jeff returned to Earth and fought crime as the Man of Brass.
During a battle on the Moon against mad renegade U.S. General Aldous Renner, Jeff sacrificed his life to save Earth. The time line readjustment that followed Wampus' defeat on Labyrinth meant that he lived on, having defeated Renner before he left Earth. With the support of General McBride, Jeff made his identity public, and later became a founding member of the Hexagon Group.
Jeff married his girlfriend Mary, and fathered a daughter, Kathryn (a.k.a. Plasma). As was his fate, Jeff Sullivan eventually died again on the Moon, fighting his arch-enemy the Necromancer alongside the Strangers in a heroic battle to save Earth. But once again., thanks to the Gods of Heliopolis, Jeff survived death and has returned to the Group.
Jeff has two brothers: Fred "Blackie" Sullivan, a supervillain now reformed, and Douglas Sullivan, MD.