The Duke of Sto Helit is a key character in the novel Mort . The Duke is the brother of the monarch of Sto Helit, King Olerve the Bastard, and the uncle of Princess Keli. He has aspirations to the throne of Sto Lat, wishing to combine it with Sto Helit to make one country under his rule. He starts the novel in the 5th position to the throne and, through his careful application of poison quickly moves up to the number 2 spot. After assassinating the King, which sets the events of the novel in motion, he appears to be trying to win Princess Kelli over to marry her and unite the countries in that fashion, but quickly abandons that plan, deciding he would rather rule alone. He sends another assassin to kill the princess in her sleep but she is saved by Mort who kills the assassin instead. However this causes problems as Keli was destined to die and Mort's actions cause time to rebel creating two different presents, At Keli's coronation the Duke attempts a second assassination but this fails as she is transported to Death's Domain by Mort and Ysabell. The Duke is later killed when his Life-timer is destroyed during the duel between Death and his apprentice.
Despite his evil intentions, the Duke was destined to have united all of the Sto Plains duchies and small kingdoms into a large single Kingdom. In order to appease the Gods who rewrote time at the end of the novel Death charges Mort, Ysabell, Keli and Cutwell with ensuring that this future comes to pass. They appear to have succeeded in this as in later novels Queen Keli is now known as 'Her Supreme Majesty, Queen Kelirehenna I, Lord of Sto Lat, Protector of the Eight Protectorates and Empress of the Long Thin Debated Piece Hubwards of Sto Kerrig.'