Leo is the name of several super-villains, all of whom are members of the Zodiac organization in the Marvel Universe.
Daniel Radford
Daniel Radford was the first person to take on the role of Leo.
Origin
A criminal recruited by a mysterious man named Taurus helped form the criminal organization known as Zodiac.
Not much is known about his early life, but it can be assumed that Radford was a criminal who had been approached by Taurus at some point to join his Zodiac cartel. He was put in charge of the Zodiac's Los Angeles branch in the guise of Leo, with his real identity hidden from the world, including all Zodiac members save for Taurus.