James Gunn released a page or two from his Guardians of the Galaxy script featuring the encounter between Ronan, Thanos, The Other and Nebula.
Gunn tells Vulture that writing Thanos was the hardest part for him.
There’s pressure with Thanos because you’re setting up this gigantic character that, in one way, isn’t really a part of your movie. His presence doesn’t really serve being in Guardians, and having Thanos be in that scene was more helpful to the Marvel universe than it was to Guardians of the Galaxy. I always wanted to have Thanos in there, but from a structural standpoint, you don’t need him. So that’s part of it, and then part of it is the fact that you’re setting up this incredibly powerful character, but you don’t want to belittle the actual antagonist of the film, which is Ronan. You don’t want him to seem like a big wussy. So how do you make that work?