Grandmaster (Marvel Cinematic Universe)

The Grandmaster is the secondary antagonist of the 2017 superhero movie Thor: Ragnarok. He is the ruler of the planet Sakaar who enjoys putting life-forms into gladiatorial fights for his own amusement.

He was portrayed by Jeff Goldblum.

Enslaving the Hulk
Starting out as the tyrant of Sakaar, the Grandmaster dedicated much of his desire to win the people's hearts by using different life-forms in a gladiatorial event (known as the Contest of Champions) held in a large arena. He is aided by his personal bodyguard Topaz, and took in a sole Valkyrie dubbed 142 as a new bodyguard following the massacre of Valkyries committed by Hela (the Asgardian Goddess of Death). The Grandmaster even got 142 to successfully capture the Hulk (who exiled himself from Earth following the deaths of Ultron and the Ultron Sentinels), and he made Hulk his new champion due to the latter's super strength that has admired much of the Sakaarian people.

Enslaving Thor
When Thor and Loki end up being banished from Asgard by Hela, they end up crash-landing on Sakaar, where Thor is enslaved and becomes a gladiator while Loki managed to win the Grandmaster's favor to become an ally of his. As the Grandmaster and Loki arrange a fight between Thor and the Hulk, the Grandmaster informs Thor that he will grant his freedom if he defeats the Hulk. Despite some reluctance, Thor almost defeats the Hulk, but the Grandmaster secretly sabotages the fight to ensure the Hulk's victory, as he has no intention in setting Thor free.

Facing a Revolution
Eventually, Thor manages to escape from confinement and freed the Hulk from the Grandmaster's control by using a recording of Black Widow. Outraged by this, the Grandmaster orders 142 to capture both Thor and the Hulk, but after reliving the deaths of her fellow Valkyries (thanks to Loki's magic), 142 decides to help Thor in defeating Hela, even capturing Loki to prove her goodwill.

Working together, Thor, Hulk and 142 staged a revolution against the Grandmaster and his forces by freeing the other gladiators from confinement. Thor, Hulk and 142 then head over to Asgard through a wormhole in order to save the surviving Asgardians from Hela and her army of Berserkers, even Loki and several gladiators provided one of the Grandmaster's giant ships to evacuate the Asgardians as Loki summons the fire demon Surtur (per Thor's orders) to destroy all of Asgard, killing Hela and the Berserkers in the process.

The Grandmaster is last seen confronting his own subjects, who are still fighting against the revolution caused by the gladiators.

Trivia

 * The Grandmaster happens to be the brother of the Collector, who appeared briefly in Thor: The Dark World and Guardians of the Galaxy.