Thor: Ragnarok

Odin dies, releasing Hela, Goddess of Death — his firstborn, and the truth about Asgard's violent founding. She shatters Mjolnir and takes Asgard. Thor is stranded on the junk planet Sakaar, ruled by the Grandmaster, where he's forced to fight Hulk, who has been there two years as a gladiator.

How was Hela imprisoned, and why? She was Odin's executioner during the conquest of the Nine Realms, and her power grew alongside Asgard itself. When Odin decided to stop conquering, she refused. He couldn't kill her, so he banished her to Hel and bound the imprisonment to his own life force — then erased her from history, painting over the murals of the conquest with images of peace. She's released the instant he dies, which is why his death opens the film.

How does she destroy Mjolnir? Thor throws it at her. She catches it one-handed — which nothing else in the franchise had managed — holds it, and closes her fist until it shatters.

"Worthiness" is Odin's enchantment, and Hela predates and outranks it. It's also where Thor learns his power was never in the hammer.

Who is the Grandmaster, and how did he get Hulk? An Elder of the Universe — same ancient species as the Collector, and stated to be his brother. He rules Sakaar as a hedonistic dictator running gladiatorial games.

He didn't capture Hulk; Hulk crashed there, was found, and became reigning champion, which the Grandmaster adores. Thor is captured on arrival by Valkyrie, a scrapper who sells fighters to him.

He never "goes missing" — his own people stage a revolution at the end and he emerges from a crashed ship trying to talk his way out. He hasn't appeared since.

How does Hulk control himself here? He isn't being controlled. Hulk has been Hulk continuously for two years without once reverting to Banner, and has developed speech, preferences, and an ego. Banner isn't in charge — Hulk simply has enough autonomy to hold a conversation.

The permanent merge into "Smart Hulk" happens later, between Infinity War and Endgame.

Thor escapes with Hulk, Loki, and Valkyrie — the last of Odin's elite guard, an alcoholic in exile after Hela slaughtered her sisters. They realise Hela draws her power from Asgard itself, so the only way to beat her is to destroy Asgard. Thor releases the fire demon Surtur and lets the realm burn. Asgard is a people, not a place.

Thor loses an eye and gains a throne.

Why does Loki take the Tesseract, and why does he come back? He takes it from Odin's vault opportunistically — Thor sent him to fetch Surtur's crown, and he grabs the Tesseract on the way out because it's leverage and because he can.

He returns with a stolen ship to evacuate the Asgardian refugees. It's the first genuinely selfless act of his arc, and Thor's reaction — surprised, then quietly moved — is the payoff of five films.

The prophecy is Ragnarok itself: Asgard's foretold destruction by the fire demon Surtur. Thor's realisation is that it isn't a disaster to prevent but the only way to kill Hela, since her power comes from Asgard. So he deliberately triggers it.

Important: this is not how the Loki of the TV series got the Tesseract. This Loki dies in the opening of Infinity War. The one who is alive today is a 2012 variant who branched off during Endgame's time heist — see Part Seven.

The ship of refugees is intercepted in the final seconds. That interception is the opening of Infinity War.