For 10 points--name this demon, the king of the Rakshasas and the villain of the Ramayana.
He had ten heads and twenty arms, and because of a gift he had once received, he could not be harmed by gods or most living creatures.  However, because of his arrogance, he had forgotten to ask for immunity from humans or monkeys, and he was ultimately destroyed by an army jointly led by the monkey-king Sugriva and one of the avatars of Vishnu.  For 10 points--name this demon, the king of the Rakshasas and the villain of the Ramayana.
He had ten heads and twenty arms, and because of a gift he had once received, he could not be harmed by gods or most living creatures.  
Ravana