Conversation so far:
who is tom ellis in once upon a time
Tom Ellis is an episodic actor on Once Upon a Time, portraying the role of Robin Hood in Lacey.
when did the show once upon a time premiere
Once Upon a Time is an American fantasy adventure drama television series that aired on ABC from October 23, 2011 to May 18, 2018.

Question: what is the premise
Self-contained rewrite: what is the premise of the show once upon a time