Cul was the older brother of Odin, and All-Father of Asgard before he was overthrown and locked away by Odin thousands of years ago in the depths of the Marianas Trench on Earth to prevent him from returning. He was guarded by magic and three large sea serpents. However, he was finally freed when Sin (the daughter of the Red Skull) was able to lift the Hammer of Skadi and free The Serpent from his ocean prison. He claims that he is the true all father of Asgard and brother to Odin. He wanted revenge due to the fact that Odin locked him away from his right as the true King of Asgard. As a result, he summons and dispatches seven hammers to choose people to become The Worthy where they land in various places on Earth. He planned to use to The Worthy to increase his power by making them spread fear across the globe
He is later seen overseeing the construction of a Nazi army led by Skadi and sending telepathic messages to his Worthy, encouraging them to cause as much chaos as possible. He later summons forth the rest of his servants and builds a fortress on Earth where, in a more youthful form, faces off against Thor. It is revealed early in their short confrontation that The Serpent is the one Thor is fated to die in battle with as prophesied instead of the son of Loki, Jörmungandr, the Midgard Serpent. Cul transformed into a giant serpentine dragon and he battled Thor, who was equipped with the Odinsword. Thor eventually defeats The Serpent by driving the sword through his head. The Serpent dies, and Thor dies shortly after. Odin carries the body of Cul to Asgard Space where he promises to watch over him for eternity.
The Serpent was created for use in Marvel comics by Matt Fraction and Stuart Immonen. His first appearance is in Fear Itself #1- The Serpent, while his death occurred in Fear Itself #7- Thor's Day.
Appearances in Other Media
Guardians Of The Galaxy (TV Series)
The Serpent makes several appearances in the most recent season of the Guardians of The Galaxy TV series. He is seen taking the throne from Odin during his Odin Sleep and using Asgardians' life force to power himself.
The Serpent is shown to be very intelligent, and does not fear many. In the series we see him go toe to toe with high powered beings like Thor and Thanos. He only seems to fear Hela, who has bested him in the past using a sword by the name of Dragonfang. The Serpent is defeated by the Guardians by the end of the series.