Darden, from Savage Empire
Darden had managed to usurp the power in the Urali Tribe by removing the statue of Fabozz to a guarded location, taking away his guidance of the tribe. By holding Fabozz under his control, he had managed to rule as an absolute dictator, forcing the tribe into raids against the other tribes with threats. Otherwise Darden would use Fabozz's control over the Tyrannosaurus to make it eat the tribe's people.
The Avatar met him almost right away in Savage Empire, when he kidnapped Aiela before the hero's very eyes. It turned out that he was Aiela's unwanted suitor. The Avatar could do little as Darden, having the advantage of a huge dinosaur, beat him soundly.
Darden locked Aiela into a cell in his tribe's land, trying to buy her love with the Kotl Gem. However, she was only disgusted with his offer. When the Avatar came to the rescue, he challenged Darden to a man-to-man duel. Without the support from his men (because the Avatar had earlier freed Fabozz), Darden was easily defeated, and the Urali accepted the outcome of the duel eagerly.