A vast rot deformed champion of Nurgle who’s left side is a swirling mass of seven tentacles undulating around a central brutal snapping beak. He is clad in foul leather and cracked plate armour including a helm with a single horn. 
He was once a tribal chieftain dwelling on the coastline of the Ocean of Blades but during the Age of Chaos he sought to impress the new gods by leading his fleet to slay a vast rot kraken. During the battle, the great beast destroyed his fleet and dragged him under the waves, but he fought on to the last, stabbing it even as it did so. [1a]
Noticing him, Nurgle granted him dominion over the kraken, Spumes own form swelling and transforming to partially mimic the creature. With his surviving crew and ships transformed as well, Gutrot became a powerful force in the service of the lord of flies, his flagship – a gargantuan rotting hulk now perched atop the kraken itself. [1a]
In the Age of Sigmar he fought Lorrus Grymn of the Steel Souls atop the Profane Tor and was later comprehensively defeated after the closing of the Genesis Gate by the goddess Alarielle and he was thrown into the garden once more. 
There for a time he commanded a black galley searching the swamps for lost souls drawn into the garden. Finding the stormcast Lorrus Grymn alone in the garden he captured him as a prize, seeking approval once more from his god. He enlisted the assistance of the witch Urslaug and in turn discovered her betrayal in time. Eventually he found his way to gift him to Father Decay, Lord High Admiral of the Plague-Fleets at the heart of the garden, the Inevitable Citadel itself. In the ensuing fight with the rescuers led by Gardus Steel Soul he was struck and wounded by a star fated arrow. 
Later in the age he attacked the city Hammerhal Aqsha with a powerful force including the Drowned Men and the Hands of Filth and although they were beaten back, plague and disease were spread through the outer districts of the city. [1b]
Like all rotbringers, Gutrot is unnaturally resilient, in combat he relies on his axe as well as the tentacles and maw of his left hand side. 
He commands vessels in the name of his god, their number and nature determined by his present standing with Nurgle. The kraken-flagship, Lurska  and his other galleons can produce copious amounts of slime that enable them to sail over land as easily as oceans,[1a] they can even take to the skies on pox-clouds! 
Proud and noted to possess boundless confidence. [1a]
|Did ye think me dead, then after the dirgehorn blew its last note. Almost was. But I’m made of sterner stuff than that. Blessed of Nurgle, I am.
~Gutrot to Lorrus Grymn.
The novel Plague Garden describes his early history somewhat differently as he enters Nurgle’s garden after the pursuit and capture of a Abak treasure ship heading for Sartos whose captain was a champion of Nurgle. The god himself drew the ships into his realm and only Spume flourished on the plagued seas that they found themselves sailing. Finally he reached the citadel of Nurgle and professed his loyalty. 
- 1: Battletome: Maggotkin of Nurgle (2018)
- 2: Plague Garden (novel) by Josh Reynolds