What happened with the Tesseract?
Did Loki steal it at the end of Thor: Ragnarok?
Did Loki steal it at the end of Thor: Ragnarok?
Towards the end of Thor: Ragnarok, both Thor and Loki realize that they need to actually fulfill the Ragnarök prophecy in order to defeat Hela, and to save the Asgardian people.
To accomplish this, Loki was sent to Odin's vault to place Surtur's helm on the Eternal Flame. When walking around down there, Loki notices the Tesseract, but is never shown actually taking it.
However, in the first few moments of Avengers: Infinity War, Loki is shown with the Tesseract in possession. IIRC though, when Loki reveals to have the Tesseract, Thor acted surprised, and so, it would seem that Thor didn't know Loki had it.
So, did Loki take the Tesseract at the end of Thor: Ragnarok? Yes. But, was it stolen? Depends on if you consider not telling Thor to be stealing or not.
Yes - it's shown in Avengers: Infinity War that Loki has it, right up until
Thanos kills pretty much all the Asgardians and takes it from him.