Duke Sigmund Igthorn is the main antagonist of Disney's 1985-91 television series Adventures of the Gummi Bears. Duke Igthorn was once a knight of Dunwyn who was exiled for conspiring against King Gregor. At an unknown point afterwards, he took control of a rundown castle called Drekmore and its resident pack of Ogres. Since then, he has constantly conspired to usurp King Gregor and rule Dunwyn himself. He has a twin brother, Victor Igthorn, who is a brave knight who fights evil. It is implied at several points that Duke Igthorn's father had attempted to control Dunwyn, and raised one of his sons to do the same.
Igthorn is very bad-tempered and a schemer. He is competent enough to gain temporary success in many of his plans, but his success is always short-lived. He later develops a crush on fellow villainess Lady Bane, but his feelings are unrequited.
Despite the fact that he has many Disney Villians' attributes, such as being full of himself, Duke Igthorn is also somewhat cunning and a fairly skilled commander. Because of his superior physical strength and command of Ogres, the Gummi Bears, as well as King Gregor, consider Igthorn to be a serious threat to their respective homes.
Igthorn is one of only a handful of humans, who know of the Gummi Bears' existence.
Duke Igthorn serves as the series' primary antagonist. He leads a group of Ogres, who are extremely loyal and physically strong, but very stupid. However, Toadwart, a smaller and slightly more intelligent Ogre, serves as his lieutenant and personal bootlicker.
In the series' premiere episode "A New Beginning", Duke Igthorn is using a gigantic catapult to tear down Castle Dunwyn. When the Gummi Bears attempt to thwart Igthorn's plan, they inadvertently expose themselves to him and thus prove their existence. From that point forward, Igthorn makes it a point to try and capture the bears in order to torture secrets out of them, as the ancient Gummi technology could be advantageous in getting Igthorn to capture Dunwyn.
Often the main purpose of Igthorn capturing Gummi Bears, is in order to gain a steady supply of Gummiberry Juice, as it provides humans with temporary super strength. Initially, Grammi Gummi, the primary holder of the secret recipe, is able to trick him multiple times with sabotaged preparations, but Igthorn eventually grows wise to that and uses test subjects before accepting another forced preparation.
In the episode "King Igthorn" (which is considered to be the show's series finale), Duke Igthorn suddenly disappears without explanation, and Castle Drekmore lies unattended for nearly a year. Believing him to be gone, the Gummi Bears send a message to the Great Gummies across the ocean telling them that it is safe to return. However, Duke Igthorn suddenly reappears, destroys Gummi Glen, and conquers Dunwyn. However, the Gummi Glen Gummies, with help from the Ursalia Barbics, are able to stop him.