This article contains spoilers for King In Black: Planet of the Symbiotes #1 by Clay McLeod Chapman, Frank Tieri, Danilo Beyruth, and Guiu Vilanova.
Marvel's King In Black event has revealed Carnage's ancestor Cortland Kasady is even worse than he is. Cletus Kasady is one of the most brutal villains in the Marvel Universe. He's a homicidal maniac, a serial killer who rejoices in bloodshed, and who was unfortunately made even more dangerous when he bonded with a Klyntar symbiote, offspring of Venom. He's most famous for the Maximum Carnage event back in the '90s, in which he led a group of sociopaths on a riot through New York City, and came close to breaking Spider-Man's very faith in humanity.
Frank Tieri and Angel Unzueta's Ruins of Ravencroft: Carnage one-shot revealed madness runs through the Kasady bloodline. He is descended from Cortland Kasady, America's first serial killer in the Marvel Universe, who arrived in the New World in the 1660s. He and his family settled in the area around what would become the Ravencroft Institute, and one day Cortland's wife fell prey to a sinister cult dedicated to the dark god Knull. Cortland rescued his beloved Molly, but unwisely stumbled into a shrine dedicated to Knull, and he went on a bloody rampage. Presumably, the madness of Knull passed on through his bloodline.
And now Cortland Kasady has returned in King In Black: Planet of the Symbiotes #1. Cortland's god Knull - the God of the Symbiotes - has come to Earth, seeking to destroy all light and life. The issue sees Knull discover the body of Cortland Kasady hidden in the labyrinth beneath Ravencroft, and he declares Cortland his greatest servant. "In all my eons of existence," Knull declares, "in all my countless travels... none spread more death and destruction... none spread more darkness in my name... than he did." Pleased with Cortland's service, Knull bonds Carnage's ancestor with a symbiote and effectively resurrects him as a new symbiote villain, who he dubs Plague.
Knull's statement is a disturbing one because it's important to remember Carnage himself became Knull's servant - one the God of the Symbiotes was so pleased with, he avenged by tearing the Sentry in half. But according to Knull, even Carnage pales in comparison to his ancestor Cortland Kasady, the first serial killer of the New World. And now, of course, Cortland is back.
Kasady appears to have been granted the power to steal the life-force of those around him, which seems appropriate for a reanimated corpse. It's less brutal and visceral than Carnage, but potentially even more dangerous, because it means Plague doesn't even need to touch you in order to kill you. Marvel's worst serial killer is more dangerous than ever before thanks to the King in Black.