What was the back story on Eragon's sword Zar'roc?

Morzan, the rider, had the sWord Zar'rok formed from the elven master forger, and was given to Morzan just before he betrayed the riders. Then, when Brom killed him, he stole his sWord which was supposed to be given to Murtagh, but then gave it to Eragon because he knew that he has more supposed to have it than Brom.