I just like to think that the casting process went like this:
"Hey Peter, we'd really like you to play a character in the new film."
"Perhaps, what's the character?"
"Well... you'd be playing a dwarf who helps Thor."
"A dwarf? I'm a serious actor and I don't want to be typecast like this."
"Oh no, you'll be 15 feet tall."
"...Deal."
Peter: "fuck yeah"
"Hey Peter, we'd really like you to play a character in the new film."
"Perhaps, what's the character?"
"Well... you'd be playing a dwarf who helps Thor."
"A dwarf? I'm a serious actor and I don't want to be typecast like this."
"Oh no, you'll be 15 feet tall."
"...Deal."