In Sundown's first life, he was one of the Buffalo people, who "were the strongest warriors ever known. Intuitive. Brazen. They were fearless. Their job was to protect all of the people, especially those charged with our souls." He was also one of the Guardians. He fell in love with one of the Butterfly people, but she was already engaged to Coyote. Coyote killed him out of jealousy, but he was reborn again and again, becoming a better man until he was worthy to unite with Butterfly.
In Sundown's last human life, he was a gun for hire. The lawmen said William Jessup Brady was called Sundown because that's when he did his best work. The truth is that his Cherokee mother named him Manee Ya Doy Ay, which means sundown in her language. He was ready to give up his gunslinger ways on his wedding day, but his best friend Bart shot him in the back outside the church. Bart then killed the priest and the bride's father and raped the bride (Butterfly reincarnated as Matilda Aponi). Sundown eagerly took Artemis' offer to become a Dark-Hunter in exchanged for twenty-four hours of vengeance against Bart.
More than a century later, Sundown met Matilda's descendant Laura and befriended her. He was also kind to her daughter Abigail, who was another reincarnation of Butterfly. He believed that she had been murdered along with her mother until she showed up in Las Vegas and tried to kill him because she thought he had killed her parents. They both eventually learned that Coyote was the real killer. Abigail and Sundown faced off against Coyote and broke the curse that had kept them apart for so many lifetimes. They married and Nick gave him his soul back, but he decided to keep it until they defeated Coyote once and for all. However, sometime between the events of Retribution and Time Untime, they changed their minds and Sundown retired. Abigail gave birth to a baby girl they named after Ren.