Sebulba is a Dug podracer from Malastare, the reigning champion of the Mos Espa circuit and Anakin Skywalker's rival in the Boonta Eve Classic in The Phantom Menace (1999). Lewis Macleod voices him.
A sport with no rules worth the name
His function in the film is to establish that podracing is lethal and unpoliced. He sabotages competitors' engines, rams them off cliffs and deploys a concealed flame vent from his own splitter, and the crowd's reaction tells you this is understood as technique rather than cheating. Anakin's win therefore means something specific: not that he is faster, but that he survived someone actively trying to kill him.
The Dug
The species walks on its forelimbs and handles things with its hind limbs, which is a genuinely strange piece of creature design and one of the few in the prequels that reads as alien rather than as a person in a suit. It also makes his podracer's hand-controls-with-feet cockpit make sense.
Later
He returns in The Clone Wars and in the Star Wars: Racer games, where he is the boss opponent, and he remains the reference point whenever later material wants a podracing champion.