In the Marvel Cinematic Universe (MCU), Thanos was killed by Thor in the film “Avengers: Endgame.” After the events of “Avengers: Infinity War,” where Thanos successfully obtained all the Infinity Stones and wiped out half of all life in the universe, the Avengers sought to undo his actions and bring back their fallen allies.
In “Avengers: Endgame,” the Avengers traveled through time to collect the Infinity Stones before Thanos could obtain them. However, Thanos discovered their plan and attacked the Avengers in an attempt to regain the stones. During the final battle, Thor, wielding the Stormbreaker axe, launched a surprise attack on Thanos and impaled him, fatally injuring him.
It’s worth noting that in the original Marvel Comics, there have been multiple instances where Thanos has been killed or temporarily defeated by various characters. The specific circumstances and characters involved in Thanos’ defeat can differ depending on the comic book storyline being referenced.