Judge Mortis was one of the Dark Judges from the parallel world known only as Deadworld, he symbolised Famine and pestilence, his cold touch could rapidly age people to death. He was once a human Rookie Judge but was transformed by black magic into the death Judge Mortis. He has clashed with the forces of Mega City-One on many occasions.
Having sensed Death's peril after he is trapped in the body of Psi-Judge Anderson after she sealed herself in Boing!, Mortis, along with Fear and Fire crossed the dimension warp to rescue him. Once Death is released from imprisonment and gains a new body, Mortis and the other three Dark Judges continued their 'judgement' upon Mega-City One claiming thousands of victims.
Dredd and Anderson intervened, and pursued the Dark Judges back to Deadworld using a Dimension Jump Globe liberated from the Dark Judges. There, the spirits of the Dark Judges' millions of victims flowed through Anderson and seemingly extinguished their spirits forever.