Sss-Thss was a powerful Slithzerai King in the Avernum series. He serves as one of the three primary antagonists of the original Avernum and its remake, Escape from the Pit, the other two being his master Grah-Hoth and Emperor Hawthorne III.
Sss-Thss was a powerful and deadly foe to Avernum during its early years. For years, the Slithzerai and the Avernites fought over the scant resources of Avernum, but it was Sss-Thss who escalated the conflict into all out war. Uniting many Slith tribes under his banner, Sss-Thss raised a massive army and began launching raids and attacks against Avernum with the intent of taking the Underworld for himself. He was greatly feared by the Avernites, both due to his own power, and the seemingly supernatural rage that consumed his forces whenever they went into battle.
Eventually, a group of Avernite adventurers slowly began to turn to the tide, managing to achieve numerous victories against Sss-Thss's forces, destroying several of his outposts and fortresses and slaying many of his generals. As the adventurers fought against the enemy Slith, they made a surprising discovery: There were in fact Slith who refused to follow Sss-Thss and were willing to aid the Avernites.
The leader of the peaceful Slith revealed to the adventurers the truth of Sss-Thss's rise to power. Sss-Thss had made a pact with a power Demon in order to gain untold power. He then used his new power to infect most of the Slith with his new master's demonic power and fury, which explains the mindless, almost feral loyalty and power of his followers.
Soon afterwards, the adventurers were commissioned by Micah, King of Avernum, to launch an assault on Sss-Thss's palace and slay the warlord once and for all. The heroes braved through Sss-Thss's mightiest champions before confronting the Slith King himself. Sss-Thss mocked the heroes, claiming that with the power his Demonic master has granted him, nothing would stand in the way of his conquest. A brutal, harrowing battle ensued, during which Sss-Thss called upon the last few defenders of his palace to defend him. However, in the end, the adventurers finally slew Sss-Thss, ending his reign and lifting the Demonic curse he had placed on the Slith.
However, Sss-Thss's death was quickly sensed by his Demonic master, who turned out to be the Archdemon Grah-Hoth. Infuriated by the loss of his "pet", Grah-hoth launched a demonic counter attack on Avernum.