Robert Castell was a Hollywood actor who was hired by Booster Gold to don a costume and act like a super-villain, named Manthrax, in a staged attack on Metropolis. Booster's intent was to defeat Manthrax, thereby making himself look heroic in the eyes of the populace. The ploy failed however when Ralph Dibny, the former Elongated Man, learned of Booster's secret deal with Manthrax and publicly exposed him.

  • Booster Gold calls Manthrax "Bob" in 52 #6 and Manthrax corrects him and states that his name is "Bill"; an issue later, Manthrax calls himself Bob Castell.