Mercury is one of the team of Metal Men created by Doctor Will Magnus. Like the other members of the team, he is powered by a "responsometer", a nuclear powered microscopic activator. This device not only animates his body, but endows him with a distinct and decidedly human personality.
Mercury is proud, big-headed and egotistical. He will repeatedly tell anyone who cares to listen that he is the only metal that takes liquid form at room temperature. While that fact can be annoying, it can also be useful, as Mercury in his liquid form can get the team out of tight situations.
During the events of 52, Doc Magnus is unable to get his Metal Men working again. He is able to switch Mercury on to help him escape from the conspiracy that is kidnapping mad scientists around the world.