Pestilence

Pestilence is a mutant and one of the Horsemen of Apocalypse.

Biography
The old woman who would become Pestilence was one of the Morlocks back when they kidnapped Cyclops.

She was tricked by Apocalypse into thinking she was being given a cure for her mutation. She seems not to get along with fellow horseman War.

In the Comics
Her Morlock name is Plague.