NOTE: This article is about the incarnation of the Grandmaster from the Marvel Cinematic film series. The mainstream version can be found here: Grandmaster (Marvel).
I just, I gotta say... I'm proud of you all. This revolution has been a huge success. Yay us! Pat-pat on the back. Pat on the back, come on. No? Me too, because I've been a big part of it. Can't have a revolution without somebody overthrown. So, uh, you're welcome. And, uh, it's a tie.
~ The Grandmaster after being overthrown by the rebels.
The Grandmaster is a recurring antagonist of the Marvel Cinematic Universe, serving as a minor character in 2017 Marvel film Guardians of the Galaxy Vol. 2, and later as the secondary antagonist of the 2017 Marvel film Thor: Ragnarok. He is the ruler of the planet Sakaar who enjoys putting life-forms into gladiatorial fights for his own amusement.
The Grandmaster makes a cameo appearance during the film's end credits, where he is shown dancing alongside the Guardians following the death of Ego.
In the film, 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 two years ago), and he made Hulk his new champion due to the latter's super strength that has admired much of the Sakaarian people.
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 manages to win the Grandmaster's favor and becomes 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 by using the paralyzing chip in his neck to ensure the Hulk's victory, as he has no intention in setting Thor free.
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 action, the Grandmaster orders the Sakaaran Guards 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. After sending Topaz to her death, Thor, Hulk and 142 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.
Following the film's end credits, the Grandmaster is last seen being confronted by several of the rebels, who have now overthrown him after defeating his forces. He attempts to appease the rebels by taking credit for the revolution and claiming that a revolution cannot be had without having someone to overthrow, declaring the revolution "a tie". However, it is quite clear that the rebels are not convinced by this, much to the Grandmaster's distraught. It can be implied that the Grandmaster is either imprisoned by the rebels or possibly executed.
The Grandmaster addresses the Sakaarian crowd on the start of the Contest of Gladiators.
The Grandmaster's zealous stare
The Grandmaster having an amusement as the Contest of Gladiator was about to commence until a major surprise happened.
The Grandmaster watches in shock and confusion in which he hears Thor screams in joy upon seeing the Hulk while Loki watches in subtle nervousness which recalls his encounter with the Hulk during the Battle of New York.
The Grandmaster pardons his cousin Carlo before gleefully executing him using a Melt Stick with Topaz watching the execution at his side, much to Thor's horror.
With Topaz at his side, The Grandmaster threatens Loki and 142 to find Thor and Hulk after the latter escaped from imprisonment.
The Grandmaster making an announcement to the citizens of Sakaar as he informs them of Thor's escape and urging them of stopping him.
The Grandmaster declaring the Revolution a tie as he confronts his rebellious subjects and proposes to them a neutral compromise.
The Grandmaster happens to be the older brother of the Collector, who appeared briefly in Thor: The Dark World and Guardians of the Galaxy. Their relationship is also the same in the 2010 Marvel Animated Universe.
Unlike most of the traditional villains in the Marvel Cinematic Universe, The Grandmaster (alongside the Collector) is considered to be a unique type of villain as he had shown no hatred or animosity towards Thor, 142, Loki or Hulk/Bruce Banner (the same action that was shown by the Collector towards the Guardians of the Galaxy), had a sense of humor as well as eccentric qualities and mannerisms. Despite his villainous motivations he can't be considered as a major threat.
The Grandmaster takes the role of The Red King but unlike the Red King, the Grandmaster is portrayed for humor and comic relief instead of being an overly serious threat.
The Grandmaster also takes the role of Mojo, since ther rights to the Mojoverse are currently held by 20th Century Fox.
At the end of the film when he is trying to appease the rebels, the specific group he addresses is a cannibalistic scavenger faction seen earlier in the film, so there is also a chance that they killed/ate him.