Stephen Bishop, and the story is that was his actual #1 guitar. As the story goes, Belushi didn't know it was his favorite and ad libbed the smashing bit. I don't remember the details, but as I recall, Belushi made amends (or tried to).
Not quite similar to Kurt Russell smashing the 19th century Martin in Hateful Eight - that was supposed to be a prop guitar, but someone made a mistake and left the real thing, and it got destroyed.
We almost saw that happen at Experience one year. For whatever reason, Paul had his team do a replica of a '58 or '59 Les Paul. They looked identical, and Paul said they did it only to prove they could do the replica thing, but they didn't really want to. Then he said, "Should we run it through the bandsaw?" Which got a lot of applause, and just before he walked over to the saw, he turned around and said, "The fake has one screw, right?" Nope - he was holding the genuine LP.