Comic Book vs Film: How Avengers: Infinity War Is Already Different

10. Thanos' Real Motivation

In The Comics:

As already established, Thanos is driven at first by a desire to impress Death, thanks in part to Mephisto's goading. He succeeds in his mission to rebalance the universe by using the Infinity Gauntlet, but when she turns him down he continues to try and impress her (including by turning a half-dead Nebula into a trinket for her).

So basically, it's lust that drives him.

In The Film:

The whole "rebalancing the universe" story element is in there, but it's not at Death's behest. According to EW's profile on Thanos, he will be propelled to a decision to redress the balance of the universe when he sees what unchecked life can do to it.

He essentially wants to save the universe from itself, which is a far more complex and worthwhile agenda than wanting to boink the Grim Reaper. Not to mention the fact that it will give him far more depth than your usual pantomime megalomaniacs.