Grendel's History
Origins
The symbiote dragon that later became known as the Grendel was created billions of years ago by Knull, alongside a crimson symbiote dragon manifested from Knull's blood. Sent out into the cosmos, the two symbiote dragons rampaged across the cosmos for billions of years, slaughtering pantheons of gods and driving the inhabitants of countless civilizations insane before devouring them.
Viking Age
In the sixth century CE, the two symbiote dragons arrived on Earth and established a lair in a cave hidden behind a waterfall in Denmark. They embarked on a campaign of slaughter to subjugate the planet, razing entire cities to the ground and ravenously devouring any wildlife and humans they came across. At some point following their arrival on Earth, a cannibalistic cult formed and began worshiping the symbiote dragons, erecting grotesque monuments in reverence of them.
Coming to be known as the Grendel, the black symbiote dragon - which was being remote-piloted by Knull - began laying siege to Heorot Hall. Attacked by the Asgardian storm-god Thor Odinson, the Grendel attempted to kill him but was struck by Thor's divine lightning and trapped inside a glacier; forming the basis of the legend of Beowulf slaying a dragon.
Old Norse carvings depicting this battle were made by the symbiote-worshiping cult and reveal that pieces of the Grendel's living abyss fell to earth after its defeat and bonded to human hosts, bestowing the cult with knowledge of Knull and the symbiotes.
Vietnam War
In 1965, the Grendel's frozen body was discovered by S.H.I.E.L.D., who excavated it and extracted samples of its living abyss to study. Upon determining that the living abyss could transform living beings into predatory monsters, S.H.I.E.L.D. - under direction from the US government to create a replacement for Captain America - established the Sym-Soldier Program, a super-soldier program headed by Nick Fury.
Upon realizing the Grendel was still alive, S.H.I.E.L.D. immediately began searching for a way to kill it, subjecting it to torturous experiments. However, they were unsuccessful and these efforts only sent its enraged offshoots on a killing spree in Vietnam.[8] After its offshoots were subdued, the Sym-Soldier Program was deemed a failure and shut down, with the Grendel being placed into storage in a remote S.H.I.E.L.D. facility alongside them.
Modern Era
Having appropriated the shuttered Sym-Soldier Program's research and personnel, Weapon Plus established the Weapon V supersoldier program and began using samples of the Grendel symbiote to engineer suits of symbiote bio-armor, eventually learning how to sever their connection to the hive-mind.
Following the collapse of S.H.I.E.L.D., the Grendel and its offshoots were being transported to a top-secret location to be disposed of. After Venom interrupted the transport, the Grendel was awakened by Knull and reclaimed all but one of the offshoots extracted by the Sym-Soldier Program. The Grendel began rampaging across Manhattan, withstanding attempts by the NYPD and United States Army to defeat it. Confronted by Venom and Spider-Man, the Grendel attempted to devour them and swallowed Miles, who unleashed his bioelectric Venom Blast from inside it. Destabilized, the Grendel collapsed and Knull used its living abyss to manifest an avatar. Knocking Miles unconscious, Knull reformed the Grendel around himself, Spider-Man, and Eddie Brock - distracting the latter by telling him the history of the symbiotes - and flew into space; intent on locating and recovering its missing pieces and using it to free himself from Klyntar.
After Venom merged with one of the Grendel's missing pieces, the Tyrannosaurus symbiote, it connected to the Hive-Mind and called out to Knull. The Grendel attacked Rex's base and attempted to devour Venom again, but was destabilized using the Jury's sonic grenades. Knull's manifestation managed to rip the Venom and Tyrannosaurus symbiotes from Eddie and tried to assimilate them into the Grendel symbiote, but Eddie detonated all the sonic grenades at once. With Knull's manifestation weakened by the resulting explosion, the Tyrannosaurus symbiote was able to rebel and drag him into the blast furnace; sacrificing itself to immolate the Grendel symbiote and seemingly killing Knull in the process.
Legacy
A small piece of the Grendel symbiote survived and was harvested by The Maker's organization, Project Oversight, before being stolen from his lab by the symbiote-worshipping cult and being bonded to Cletus Kasady. Cletus would go on a rampage to get enough codices to free Knull. He would finish his conquest while dying at the hands of Eddie Brock, who would absorb the codices, finally reconnecting Knull to the hive-mind and freeing him from his Klyntar.
Additional samples of the Grendel symbiote remained in the possession of the Weapon V Program, which was attacked by Carnage and shut down during his rampage; later restarted under Dr. Randall Pierce.
The offshoot that had bonded to Cletus was absorbed into the Venom symbiote by Eddie Brock, but resurfaced after a few weeks and attempted to take over him. When Eddie travelled to the Isla de Huesos to destroy it, it separated itself from him, assimilated the Venom symbiote, and attempted to take over Eddie - intending to use him to pick up where Cletus had left off. While the Dark Carnage symbiote was successful in taking over Eddie, Dylan Brock - the son of Eddie Brock, who had the power to control symbiotes - helped his father by transforming Venom into the form of a Tyrannosaurus rex. With Dylan's help, Eddie overcame the Dark Carnage symbiote's influence and separated from it, rebonding to the Venom symbiote. Although it was seemingly destroyed by Dylan, the Dark Carnage symbiote survived and left the island in the form of a shark.
