Sigthor, known as Ikuo Kiyokuni in the Japanese version, is a character in the Tag Force series.
When the player receives Sigthor's Deck Recipe in Yu-Gi-Oh! GX Tag Force, they also receive the card "The Graveyard in the Fourth Dimension". Unless partnered with the player, he partners with Joshua during the Tag Force tournament.
In Yu-Gi-Oh! GX Tag Force Sigthor's Deck, titled Third Dragon, contains many Dragon-type Normal Monsters. He can use "Heart of the Underdog" to quickly draw large amounts of them and fuse them into more powerful monsters with "Fusion Gate". In later installments, he switches to a Deck more focused on Union monsters.