Every villain is a hero in his own mind.
Actors in any capacity, artists of any stripe, are inspired by their curiosity, by their desire to explore all quarters of life, in light and in dark, and reflect what they find in their work. Artists instinctively want to reflect humanity, their own and each other's, in all its intermittent virtue and vitality, frailty and fallibility.
Loki in 'Thor' is the most incredible springboard into a sort of excavation of the darker aspects of human nature. So that was thrilling, coming back knowing that I'd built the boat and now I could set sail into choppier waters.