Y Haiku #atozchallenge

Talks backwards, he does,
And teaches, “There is no try—
You do, or do not.”

Here’s the haiku puzzle for the day in the A to Z Blogging Challenge. What character from science fiction or fantasy has a name starting with Y and is suggested by the haiku? I think this one should be relatively easy for most people, even those who are not major fans. He’s small and looks like a Muppet, but you do NOT want to get on his dark side! Know who I’m talking about? Tell us in the comments.