A Turncoat

Realistically, the Avengers, Guardians of the Galaxy and company might actually require someone who is working alongside Thanos – someone the Mad Titan trusts – to turn against him for the good of the universe.

For example, Loki may well be at Thanos’ side for the Infinity War movies, but the God of Mischief might see sense and realize that having the Mad Titan ruling the universe with absolute power would be a very bad idea.

Loki could redeem himself for all the bad things he has ever done by turning against his master and saving the universe. Something like that would go down well with the fans – with whom Loki is a big favorite – but it could be any evil ally working with the alien warlord.

Now for something that needs to happen regarding someone by Thanos’ side.