Thanos is big in terms of the way he is feared. I want to know if he is part of only the galaxy. For example, the heroes known as "The Guardians of the Galaxy" are so named because they protect only the galaxy. Think of it like this: Where does Thanos lie on the list of big villains?
Earth: The mob. I mean Hydra.
Solar System: Hydra still
The galaxy: If not Thanos then maybe Ronan
The universe: If not Thanos then maybe Celestials
The multiverse: Galactus???