Judd Fry is Carrie's ancestorHe is an unpopular pariah in town who nobody likes. One of the prettiest and most beloved people in town goes with him suddenly to the local dance, but on the night where it seems everything is going to turn good for his life, he's made a fool of in front of all his peers, ultimately driving him to a murderous rampage leading to his demise. Unfortunately he never had psychic powers, and never got his divine justice, like his future descendant will.
Jud stabs himself on purpose.Well, there was that whole "Pore Jud is Daid" song, and he was starting to seem pretty convinced that everyone would like him after he died. Since Laurey was married to Curly, maybe Jud thought he didn't have anything left to live for. Maybe he wanted to frame Curly for it as a final parting act of spite, or maybe it was just a spur of the moment decision in the middle of their fight.