Originally Posted by Mjölnir
How is it simple for him to just replace the All-father? Odin isn't exactly powerless, to put it mildly.
Otherwise I agree, Loki took out the guard that went looking for them and assumed his identity.
One question comes to mind, if Odin is in reality Loki in disguise, then why did Loki not prevent that the Aether is given away at the end? One royal order from "Odin" to keep the Aether should have been sufficient - and Loki certainly wanted to have that thing!