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So this baby named Buddy crawled into Santa's bag at an orphanage, I guess, and then he was raised by elves (including one played by Bob Newhart), and he thought he was an elf. When Buddy grows up (now played by Will Ferrell) he learns he's human, and goes to find his father, who never even knew he existed, because Buddy's mother (who died) never told the guy about the kid, I guess.
Anyway, Buddy's father, Walter Hobbs (James Caan), is a businessman, and has a wife (Mary Steenburgen) and son. At first he doesn't believe Buddy is his son, and when a blood test proves it, he still thinks Buddy is nuts. But eventually he finds out there really is a Santa Claus and all that. Oh, and Buddy falls in love with this girl named Jovie (Zooey Deschanel). I can't think what else to say except it was a funny movie. Not one I particularly cared about, but it was okay. Of course, I wasn't really paying that much attention to it, I think. It was more sort of on because my sister was watching it.... Some people liked it a lot better than I did, and I'm sure they're right. Maybe if I paid closer attention I'd like it more, but then again... like I said, I don't really care.
The movie came out in 2003, and in 2010 there was a Broadway musical based on it. In 2014, the musical was adapted into a stop-motion animated TV special, Elf: Buddy's Musical Christmas.