Bartolomeo Allen is a distant relative of Speed Demon (Matt West), born in the far future. Sent to this century so that he might escape certain death, Bart is a wild child, exultant in his speed and eternally bored with the slow-paced 20th century. Matt has placed Mercury under the care of the mysterious Caduceus, hoping that the somber and wise guru might calm Bart and give his young life focus.
Mercury is the Amalgamated version of Quicksilver (Marvel speedster) and Impulse. He only appears once and that's in the Amalgamated issue of DC and Marvel JLX. Once the two worlds where un-amalgamated, he disappeared.