Originally Posted by jmc
He's Loki, he's demonstrated in 3 movies he's has the ability produce illusions. That's not a complex answer.
It's also not an acceptable answer. How does he manage to replace Odin? It would very quickly be noticed if there was two Odins walking around in Asgard, especially when Thor comes back to talk to his father. It's obvious that something must have happened to Odin.