This page is refering to the ruler of Dys. The page for Madoc, the Winter King, can be found here.
Lord Winter is a tulpa of Jack made by Charles and Burton, but ended up being corrupted by Dr. Dee. He became known to the Caretakers under the alias of Mr. Kirke. He kidnapped Warnie so that Dee's Cabal can enter the Nameless Isles. He splits the timeline between Primetime and Dys when he either kills Jack at the Terminus (Dys) or Jack accepts him as part of himself and disperses the tulpa (Prime Time).
In the Might-Have-Been known as Dys, after he killed Jack he took on his . When he enters the story, he has been unable to take The Last Redoubt, and is kept captive in Dys by the Echthroi until he can. He hopes to use Rose to become a Dragon's Apprentice so that he can break through the city's defenses and take over. He nearly succeeded in his goal before he was killed by Rose's apprentice, Burton, who turned into a dragon.