relative pronouns - What is the subject of this sentence

I've seen this sentence in someone's facebook status but it sounds unnatural to me.

I'm the Rumplestiltskin who spins straw into gold

I thought it should be spin because the subject is I, but I'm not sure. Which one is the subject in this sentence, I or Rumplestiltskin and why?

Answer

The subject of the main clause is I. But then that subject talks about himself in the third person: The Rumplestiltskin who spins straw into gold. Spins agrees with the subject of the relative clause.