Mercury lived in the mountains with his father, Marcus Black, who was an assassin and implied heavy drinker. One night, he fought against his father and killed him. Cinder Fall and Emerald Sustrai saw their fight from afar and were hoping to recruit his father for their cause. However, due to Marcus' death, Cinder asked Mercury if he took after his father. He joined Cinder's cause and has been traveling with them since. According to Kerry Shawcross, Mercury has one of the darkest backstories, which has yet to be fully explored.