The Sith apprentice that Qui-Gon Jinn and Obi-Wan Kenobi fight together is Darth Maul. Their climactic duel takes place on Naboo in Star Wars: Episode I – The Phantom Menace.
Darth Maul was the secret apprentice of Darth Sidious, who later became publicly known as Sheev Palpatine. Sidious sent Maul to pursue Queen Padmé Amidala and eliminate the Jedi interfering with his plans during the Trade Federation crisis. Maul’s red, double-bladed lightsaber and acrobatic fighting style made him an immediate threat.
Qui-Gon and Obi-Wan initially fight Maul together in the Theed Palace reactor complex, but the battle separates the Jedi. Maul fatally stabs Qui-Gon, after which Obi-Wan uses the Force to leap from a pit, seize Qui-Gon’s lightsaber, and cut Maul in half. Maul’s apparent death becomes a major point of confusion: later Star Wars stories reveal that he survived and returned as a recurring antagonist.
Darth Sidious is the master who commands Maul, not the warrior in this duel. Darth Vader appears much later in the saga, while Darth Plagueis is connected to Palpatine’s backstory rather than this fight.