Morlocks are a group of mutant characters appearing in American comic books published by Marvel Comics. The characters are usually depicted as being associated with the X-Men in the Marvel Universe. Created by writer Chris Claremont and artist Paul Smith, they were named after the subterranean race of the same name in H. G. Wells' novel The Time Machine, but unlike in the Wells book, they are not a faceless, threatening mass of villains. They first appeared as a group in The Uncanny X-Men #169 (May 1983). Caliban appeared prior to that, but he was not yet a member of the Morlocks.
The Morlocks were depicted as an underground society (both literally and figuratively) of outcast mutants living as tunnel dwellers in the sewers, abandoned tunnels, and abandoned subway lines beneath New York City. The Morlocks were composed of mutant misfits, especially those mutants who, because of physical mutations or other conspicuous manifestations of their mutant genetics, were unable to pass as human in normal society. Subjected to hate, fear, and disgust from human society due to their "deformed" appearances, dangerous mutations, or otherwise outcast or misfit statuses, most of the Morlocks viewed humans (and even more mainstream mutants such as the X-Men) with distrust and anger, and they occasionally committed criminal or antisocial acts upon the above-ground human society.
Due to a series of tragedies, the original Morlocks no longer reside in subterranean New York City (except Marrow, who was one of the original Morlocks as a child), although a violent splinter cell Gene Nation and a comparable group called Those Who Live in Darkness have emerged. Similar groups, called Morlocks by readers and/or the X-Men themselves, have appeared under Chicago and London.
According to Callisto, she formed the Morlocks by first recruiting Caliban, and then using his power to track down other mutants who were unable to integrate into normal society. The Morlocks initially squatted in a network of abandoned, interconnected tunnels beneath Manhattan, which had originally been built as Cold War bomb shelters and then forgotten.