The Morlocks is a group of mutants with generally severe disfiguring mutations that live in the sewers. They have been known to do raids on the surface for goods they can't get elsewhere, and perform terrorist activities at times in moments of frustration and when under ill-advised influences. They live by their own codes, having a completely different culture than those above ground.
The Morlocks are founded by Callisto, as a way to hide from the judgmental humanity in saftey.
Morlocks are gathered over the years, and some are found at a young such such as a mutated, abandoned Marrow when she was a baby.
The Morlocks kidnap the X-Men member Angel, with Callispo intending to marry him. The X-Men arrive to save him, and Storm faces Callispo in single combat, defeating her. When the X-Men depart, as the new leader of the Morlocks, Storm places Callispo as defacto leader - her stand in.
Mr. Sinister attacks the Morlocks. He and the Marauders decimate the community, believing that the Morlocks are polluting the gene pool. A young Gambit is there and manages to save a four year old Marrow.
The Morlocks work at rebuilding their community.
Several years later, while still rebuilding their community, they are attacked again by Mikhail Rasputin, a powerful mutant. It is believed that everyone save Callispo and a few others, are killed in the attack, but were really transported to a pocket dimension by Mikhail's powers.
Morlocks and others live a gladiator life-style, before Mikhail takes them back to the real world. For the survivors, it was seven years, but only a year or two passed in the real world. He dubbed the group Gene Nation.
Upon their return, Mikhail had Gene Nation perform a terrorist attack in a New York Nightclub, killing a dozen or so innocent men and women upon their return. The X-Men stop them from furthering slaughtering people, and forced them to retreat to the Morlock tunnels. In a last ditch attempt to force the X-Men to surrender, Marrow wired a time bomb to her own heart. Storm, their former leader ripped out Marrow's heart to save everyone, but the Morlock lived due to having two hearts.
The surviving Morlocks again began to rebuild their community, with Callispo as their leader once more.
Roughly two years later, Callispo is injured by a government operative while on a terrorist mission, the result would kill innocents to show humanity how much the Morlocks are suffering. Marrow abandons the wounded Callispo and flees after realizing that the slaughter of innocents solves nothing. She runs to the X-Men for help, and is considered a traitor to the Morlocks.