Boris was a mobster hired by Butch Gilzean.
Boris and a few other mobsters came calling on Barbara Kean when they found out that they didn't have Penguin's support. Barbara and Tabitha Galavan killed the two men accompanying Boris and hold him hostage. Penguin and Butch Gilzean arrived at the club to find out what occurred. Barbara informs Penguin that Butch hired Boris and his men in an attempt to get him and Tabitha back together. Penguin hastily shoots Boris in the head.