Benjamin Lafitte was a vampire, turned by the ancient one known as The Old Man, who he worshiped as a god. However, fifty years ago, Benny fell in love with a Greek woman named Andrea Kormos, deciding to abandon his maker. The Old Man discovered this and killed Benny, condemning his soul to Purgatory, the realm where all monsters go when they die. Fifty years later, he helps Dean Winchester escape from Purgatory in exchange for being brought back to life, developing a strong friendship with him while there. Back on Earth, Benny decides to go after his maker, eventually killing him with Dean's help. After trying and failing to adapt to life on Earth, Benny allows Dean to kill him so he can return to Purgatory and rescue Sam. Benny, who doesn't fit in on Earth anymore, then stays behind to hold off a group of vampires so Sam and Bobby Singer can escape.
Benny is actually one of my favorite character on Supernatural. I was actually sad to him go. So it was nice to see him again when I was doing a second watch.