Sek-Duat XV is a tyrant emperor that rules over the Sandsea with an iron fist. He has ruled the Sandsea from these Pyramids. They are the home of his ancient Dynasty.
He is the current king of The Sandsea. He lives in a palace and leaves his people in poverty to die in the sands. The Sek-Duat dynasty has ruled the Sandsea with a curel, iron fist for 1500 years or more and this new emperor is more cruel and more evil than any before him, Sek-Duat XV's reign has been the most terrible of all. His deeds have finally caused a small faction of the desert people to rebel.
He hired Zhoom and paid him well for hunting down the members of the resistance forces.
He has asked the player to defeat the Sandwitch, that he claimed to "steal villagers in the middle of the night", and "to never be seen again", but, in fact, he stole a book from the Sandwitch, and he wants to use it to revive his first ancestor and eternally rule the Sandsea, using the Light Orb, and now that the Mumragons are no longer alive, the place is safe to revive him.
In the Sandsea's quest "The Traitor", it is revealed that he needs the soul of 100 men that call him "enemy", in order to revive his first ancestor.
Then in the quest "Zhowdown" he told the hero/heroine to take down Zhoom believing that he is working for the resistance and then payed Zhoom to capture the hero/heroine but in fact he was trying to take down both the hero/heroine and Zhoom by sending the Sphinxter to kill them.
Sek-Duat became a lich to receive eternal life but he also was eternally unsatisfied, like all lichs are, so he wanted to become immortal in different ways. When he was searching for a cure, he was becoming more and more cruel, and his ancestors were not hunting the Sand Elves; he was.
When he got the spell (he sent his guards the steal it) from the Sandwich, he learned that he needs 100 souls and the light orb for the spell. He then proposed the hero\heroine and Zhoom to join him, but if the hero\heroine refuse (you can't accept the offer anyway), Sek Duat battles them, and loses.
But because the people were still accepting Sek Duat as emperor and the rebels were hiding among the people of Sandsea it would be impossible to find the rebels, so he captured all of the people of Sandsea using his minions, and planned to sacrifice their souls for his immortality. But as his army is defeated, he summons the Dunelord to battle the hero\heroine and his\her titan dragon. When the Dunelord is defeated, Sek Duat's power is greatly diminished, but he was still a threat for the rebels.