Spoilers for Ragnarok will follow…
In the comic books, Thanos is enamoured of the Mistress Of Death, who’s the actual embodiment of the end of life. The Mistress Of Death is not the same as Hela, Goddess Of Death, but the MCU has changed characters before to fit a more streamlined narrative. Hela having been unveiled in the franchise in one of two films that lead directly into Avengers: Infinity War – in which Thanos unleashes great power – could suggest that, in this version of the Marvel Universe, Hela is a romantic interest for The Mad Titan.
It could be that it’s Thor’s clash with Hela on Asgard that draws the attention of Thanos in the first place. We know that the God of Thunder is on his radar thanks to the mid-credits scene at the end of Thor: Ragnarok, and Hela being the cause of that would give her greater significance in the franchise as it moves forward.
It’s entirely in keeping with Marvel’s approach to female characters in the MCU to have the first leading female villain appear at a given point specifically to serve a narrative purpose that revolves around male characters. This has been the way in which every significant female hero has been introduced, after all.
Black Widow was undercover as a Stark employee, to help Iron Man find his way to S.H.I.E.L.D; Scarlet Witch arrived with her brother, being held captive by male Hydra leaders; Agent Carter helped Captain America in his first missions; Sharon Carter helped Captain America in his later missions; Hope van Dyne helped Ant-Man become Ant-Man. If Hela is indeed the reason that Thanos has zeroed in on Thor and his group at the end of Thor: Ragnarok, then she’s a functional plot device, like her heroic counterparts – albeit one with multi-film potential.
The ending of Thor: Ragnarok makes the future unclear for Hela, though, and it’s equally possible that it’s Loki that has drawn the attention of Thanos – given that the God Of Mischief was tasked with retrieving items from Odin’s vault. If Loki is in possession of an Infinity Stone, then that would also explain the Mad Titan’s sudden arrival. In that case, Hela was purely a glorious female villain who escaped the bonds of imprisonment, took umbrage at having been erased from history by a patriarchal society, and sought to have her revenge.
That’s a far more poetic way to involve the first leading female villain in the MCU.