As for the new characters…
Dr. Bruce Banner/The Hulk (Mark Ruffalo)
Mark Ruffalo reprises the role of the MCU’s Hulk in Thor: Ragnarok. Though not his first appearance in the MCU, this is Ruffalo’s Hulk’s first Thor franchise appearance. Thor’s former Avengers ally turned foe meets him in battle in a gladiator-style arena while he is trapped on the planet Sakaar.
Thor: Ragnarok draws heavy inspiration from the comic book storyline ‘Planet Hulk’. Hulk and his human persona Bruce Banner are sure to support the new direction of the franchise as they join Thor in the fight to protect Asgard.
Hela (Cate Blanchett)
Cate Blanchett makes her MCU debut as Hela, the main villain of Thor: Ragnarok and the aggressor against Asgard on the planet Sakaar. The Asgardian Goddess of Death established herself as a more than worthy foe of Thor by shattering his hammer, Mjolnir.
Hela can summon weapons from her body, and is clearly an all powerful villain capable of flattening Asgard if Thor is unable to rally against her.
Valkyrie (Tessa Thompson)
Valkyrie makes her live-action and MCU debut in Thor: Ragnarok, portrayed by Tessa Thompson. In Norse mythology, Valkyrie are responsible for escorting the souls of warriors to their eternal resting place in Valhalla.
In the film adaptation, Valkyrie is an Asgardian warrior who works for the Grandmaster, recruiting worthy fighters for gladiator matches in exchange for hiding out on his planet.
The Grandmaster (Jeff Goldblum)
In what is possibly the most anticipated new character role in this film, Jeff Goldblum makes his MCU debut as The Grandmaster. In the comic book storylines and in Thor: Ragnarok, The Grandmaster is a powerful cosmic being with an appetite for gambling, games, and spectator sports. He is the master of a gladiator ring on his planet, Sakaar, and he arrogantly observes the proceedings from his luxury suite.
We have The Grandmaster to thank for the clash of Thor and Hulk in the arena.
Skurge (Karl Urban)
Although known in comic book storylines as The Executioner, Skurge will be an Asgardian warrior portrayed by Karl Urban in Thor: Ragnarok. Skurge is known for wielding an ax and multiple firearms.
His role in the film in a bit of a mystery at the moment, and is also most likely small.
Dr. Stephen Strange aka the Sorcerer Supreme (Benedict Cumberbatch)
As teased by the post-credits scene of the movie by the same name, Dr. Stephen Strange and Thor have met, and Dr. Strange will make an appearance in Thor: Ragnarok. Benedict Cumberbatch makes his second MCU appearance as the Sorcerer Supreme.
The length and scope of Dr. Strange’s role in the film is unknown, but will most likely be small, yet entertaining.
Korg (Taika Waititi)
Korg is another character taken from ‘Planet Hulk’ storyline’s inspiration. He is another gladiator forced into combat by the Grandmaster who will be on the side of Hulk.
Thor: Ragnarok director Taika Waititi performed this role through motion-capture technology, so it will most likely add to the humorous direction the franchise is headed in.
Surtur (voiced by Clancy Brown)
The hugely powerful fire demon from Muselheim was inadvertently revealed through Thor: Ragnarok promotional marketing and toys. Surtur is one of the most powerful villains of the Thor comic book storylines. Though the exact nature of his appearance is not known, it is safe to assume he will aid Hela in bringing about the end of Asgard. Surtur will be voiced and portrayed by Clancy Brown.
Stan Lee, Sam Neill, and Lou Ferrigno are also rumored to cameo or appear in supporting character roles.
Thor: Ragnarok is on general release in the UK from Tuesday 24th October.