Stewart Burns was the demonic main antagonist of the Buffy: the Vampire Slayer episode "Hells Bells." He was portrayed by the late George D. Wallace.
It was heavily implied that Stewart was a man who evildently angered a jilted lover back in 1914 in Chicago's South Side. A vengeance demon who works with scorned women, Anyanka, heard her desire for revenge. She turned him into a demon and banished him to a Hell Dimension. Over the course of eight decades of time, he plotted his revenge on Anya. He returned to Earth and heard about Anya's wedding to Xander Harris in the spring of 2002. This presented him a perfect opportunity.
He would arrive at the chapel in the guise of Xander's future self and claimed he went back in time to prevent Xander from making a big mistake. He showed Xander a bleak future of how Xander and Anya's relationship would take a turn for the worst. It culimated to Xander murdering his wife. That vision shook Xander to the core. He didn't arrive at the alter. After the delays a fight broke out between Xander's dysfunctional family and Anya's friends. Then Anya spotted Stewart and once she confronted him. he gloated on how he got his revenge and how he got Xander to leave her. He would then attempt to murder her. But then Buffy Summers, the Slayer herself and Xander killed him.
However, Stewart's death was sadly for Anya not in vain, for Xander called off the wedding, leaving Anya broken, sad, and alone. She became a vengeance demon for a while, Xander and Anya would months later have break up sex and would never get a chance to back together again after she died in the Battle of the Hellmouth against The First Evil. Despite the fact that Stewart died, he got his revenge.