Gutrot Spume is a Chaos Champion of Nurgle who commands the mighty Dragonbone Tribe/Fleet of Chaos Pirates and was part of the three-prong attack that comprised was the central plot of The End Times' second book. He's easily recognized by the mass of tentacles that replaces the left side of his torso.
As a child, he loved the sea. He spent his free time diving into the Sea of Claws and killing whatever he came across with a knife clenched between his teeth like a total badass. While this impressed his fellow tribesmen enough that he was made jarl of his tribe, his big ambition was to get noticed by the dark gods. That chance came when he heard of a monstrosity called the Rot Kraken. He immediately set off with his fleets to chase after it. After a long voyage through the Sea of Claws and warding off several fleets of Elf pirates, he finally found his quarry and dove after it. He thought that he could kill it easily, but he then found himself fighting for his life against the kraken's hatchlings. He was transformed into a half-man, half-octopus monster by Nurgle and when he finally emerged from those depths, he did so as a full-fledged champion.
He made it over to Age of Sigmar, where he's the leader of the warband known as the Drowned Men. Though his origin as recounted the battletome is pretty much the same, the fact that he came from the World-That-Was isn't mentioned (out of all the returning Nurgle characters, only the Glottkin are mentioned as being so). He also appeared as one of the major antagonists in the book "Hallowed Knights: Plague Garden", where he quite easily was the best character.