Slith, King of the Underworld, is the son of Ugrach, Curator of Death who was formerlly King of the Underworld. He was first encountered by Khalas at the beginnings of the War of Humanity when the Triumvirate was preparing its forces. Slith was eager to join the army of the Triumvirate and was practically forced to do so after being cast out of the Underworld by his father, who wanted nothing to do with the war. The most notable achievement of Slith's undead forces in that war was the complete decimation of Thoth's Quisalis assassins, though later he was banished along with the demon Pazuzu to the Chaos Plane.
In the year 309 AF, an unknown entity was found to have kidnapped Pandemonium, the unborn son of Aegis and Eris, and when it returned to steal the boy's twin sister, Pandora, was revealed to be Slith himself. With the God of War in pursuit, Slith disappeared from the Prime Material Plane.
He was not seen again until 326 AF, when the Darkenwood was suffering from a mysterious ailment, and Slith was revealed in an experiment conducted by Eris using the Living Spire. Slith was hiding within the Darkenwood itself, draining its essence at the behest of Sartan. It was revealed that, after kidnapping the child Pandemonium, Slith was split into two beings by the God of Evil, one half retreating to a hidden plane to lure Aegis away, the other half to the Darkenwood.
Around the year 333 AF, Slith snuck into Shallam and was able to steal a small piece of essence from the ailing Pentharian, enabling him to trap the God on a hidden plane. He later found he possessed a portion of essence belonging to both Lorielan and Mithraea as well, and set traps for the Goddesses as well. He was able to successfully trap Mithraea on the plane with Pentharian, but was defeated in his attempt to secure control of Lorielan.
In 426 AF, Slith took on the guise of Tavarius in the events of the Eternal Night. He used the Disc of the Nocturne to hold the planets Noxtra, Lunastra and Somnustra in a convergence that eclipsed the sun. He also caused all signs of the Goddess Ourania to vanish from mortal perception.
In the year 715 AF, Prince Slith appeared to challenge Thoth, slaying him in the process. The Gods then sealed him in the Halls of Thoth until his trial was held before the whole of Sapience and the Pantheon to decide his fate. It as at this Moot where the Pantheon decided his fate, but before the verdict could be reached, Slith's father Ugrach appeared to plead for his son's life. It was then that Prospero drafted an contract that would bind Ugrach to the Halls of Thoth and Slith to the Underworld as well as give dominion of the realm and its inhabitants to the Gods. After the contract was signed that gods that choose death for Slith were able enact punishment against him stripping him of his powers and abilites to where he became a shell of his former self.
With his Father removed from his throne, Slith tooks his place as ruler of the Underworld but due to the punishments of the Divine, he was unable to do it alone. A clamour of voices rose to take the position of advisor in a conflict which would be named The Underworld Rebellion. In the end Asztrik and Prioska were successful and were chosen as his advisors after the war.
Both a mystical card and a battle figurine commemorate Slith's position as Lord of Undeath.