Leech made his first appearance in Uncanny X-Men as a Morlock, a group of mutants whose deformities force them to live in the sewers under Manhattan.

X-Factor takes him and Artie in until they can be enrolled in St. Simons, a private school that willingly accepts mutant children.

[4] A nearby resident, Ida Fassbender, discovers the trio's technologically assisted jaunts, and her paranoia endangers their lives.

[volume & issue needed] This group was composed of second-generation Morlocks, the descendants of those who survived the massacre in the tunnels.

[6] Leech and Artie continued to live in the Massachusetts Academy under the care of Emma Frost and Sean Cassidy.

Back at the Academy, they encounter Howard the Duck and other allies and as a group, are attacked by Black Tom Cassidy.

[8] When Richards' family, who had previously been exiled to an alternate universe (see Heroes Reborn), return, the group was disbanded.

Leech survives and is one of the estimated 198 mutants who retained their powers after M-Day and moves to an encampment in the Xavier Institute.

[11] When an exploding supervillain causes the general public to turn on superheroes,[12] Domino, Shatterstar, and Caliban break out the 198 and take them to a bunker in the middle of the desert.

[volume & issue needed] Leech can dampen or completely suppress, for an undetermined amount of time, the powers and abilities of any superpowered beings within 50 feet of him.

This version is named Jimmy, possesses a human appearance, and was used by Worthington Labs to create a "mutant cure" before joining the Xavier Institute.