Dunno if I need to, but I will go with caution and spoiler this answer.
Spoiler
Death was a judge on his own world in his own dimension, he was a nutter that developed the ideology that crime was commited only by the living, so if everyone was dead, then there would be no crime, so life itself became a crime. He gets himself a few mates who sare as nuts as him, he meets the sisters who are basically witches. The sisters turn him nto an undead zombie, the others into Fear, who kills by fear, Fire, with fire and Mortis who kills with decay, then they kill everyone on their world. Eventually a dimesional traveller makes the mstake of showing up in Deaths dimension, who kills him, realises there are more living people out there, uses it to come to a new dimension, happens to be Dredds, turns up starts offing cits.
Cassandra Anderson is the one who in the end actually defeats Death. Death is a spirit bad guy essentially, so if they destroy his body he can always inhabit another corpse, his tag line being 'you cannot killlll what doesss not live' Anderson is PSI division, she is a psychic (I forget if they are doing that in the film) she is able to suck Death into her mind, then the other Judges incase her in Boing™, which is like a toy plastic, people get sprayed with it and then bounce around in bubbles, Anderson is effectively trapped in stasis with Death. Eventually Deaths fellow Dark Judges come from their own dimension to look for him, Death gets lose, fighty fight, once again Death gets defeated and all of them get locked up in Boing™ stasis.
In the Necropolis storyline Dredd has taken the long walk, which is the judges version of retirement, to go out into the cursed earth and carry on giving justice to the muties until they die. He is replaced by a clone of himself, called Kraken. Kraken was the product of a scheme of a previous nutter judge called Judd, a fanatic who turned traitor and grew his own clone army and tried to take over MC1. As Kraken is flawed with the Judda indoctrination, the sisters of death are able to get a hook in him and possess him. The sisters induce halucinations, but their power is weak across the dimenional divide, using as they are an ordinary women or low level psyker as a conduit, they get Kraken to sacrifice a PSI judge, Kit Agee, with her in a state of near death they are able to make the bridge as strong as it can be. They are then able to possess the entire judge force, a great many of who were on their way to take the block out where Agee was, but they are too late, they start kiling each other and Anderson ends up getting run over by a tank. She actually falls into the undercity as the roadway under the tank falls in. She enters a coma like state, while her mind calls out for help. After he thinks Anderson is dead Kraken then goes and free's Death & co, he is then against his will is turned into a Dark Judge and is forced to kill citizens, but cant stop himself.
Out in the cursed earth, the sisters appear to Dredd, their powers are limited so far out, but they are able to toast him and leave him for dead. This was a storyline that ran at the same time as Dredd called The Dead Man, tells the tale of a man who is burned to a crisp, who wakes up by a mutie village, they take him in and nurse him back to health, but he has no memory of who he is. Eventually the two stories run together and Dredd realises who he is. Was a good little twist because you didnt know it was Dredd and it came as bit of a surprise when it was revealed. With his memory back Dredd sets out back to Mega-City to take on the Dark Judges, lead by Anderson in her coma, he hooks up with former chief judge McGruder, who had taken the walk years earlier, and along with a group of judge cadets they meet in the undercity where they also find Anderson. Anderson tells them that have to kill Agee, which they do by blowing up the block she is in, sending the sisters back to their own dimension, freeing the judges, the Dark judges are then captured, except for Death who dives off a city block and vanishes, usual cliff hanger for a return type ending.
