Leech was born mutant with the powers of inhibiting the powers of other mutants next to him. If he always had the same appearance that he's now or was changed, according to the custom, by Masque, it's unknown, but his nickname reflexes his appearance. Leech seemed to live with the Morlocks in the tunnels under Manhattan since he was a baby, but little is known of him until he was taken to X-Factor headquarters, after the mutant massacre conducted by Mr. Sinister and the Marauders, Leech took part in some fights between morlocks and X-Men before, used to steal their powers, like he once did to Storm while she was flying through the tunnels. The first time he was seen by an X-Man was while Callisto was trying to marry Kitty Pryde to Caliban and she escaped. Leech was the one who found her and brought her back to safety. Remember, the sewer is not a nice place to visit, and she avoided her using her phase powers.

As he lived in X-Factor headquarters, he met his best friend, Artie Maddicks, who was a kid like himself. They, like Skids, Rictor, Boom Boom, and Rusty Collins, were sent to a private school to keep them safe, but then, Inferno began, and the demon N'Ashtir tried to kidnap them to conduct a sacrifice and open a giant gate to Limbo. Their being mutants was what the demon really needed.

With some help from one of their companions who was mutant as well, Taki, they escaped and joined the rest of the mutants to fight the hordes of demons. As the situation returned to normal (whatever it is) , both went back to the school were they got kidnapped - again -- some time later by the Gene-Nation, a group of former Morlocks ruled by the Black Beast -- courtesy of AoA -- who was willing to control the world and kill as many humans as possible. Leech was used to capture Emma Frost, not letting her use her powers. But as part of Generation X, Leech came to take her out, she kicked Leech down and vanquished easily her foes. Leech and Artie were then taken to the Massachusetts Academy and made friends with Synch and Skin, who made a house in a tree on the grotto for them to play.