As a child, Rose Canton would use an imaginary friend, "Thorn" to deflect blame for bad things that she did. Over the years, Thorn developed as a distinct persona in Rose's head. As an adult, Rose was studying biology on the island of Tashmi, where she was exposed to the sap of a jungle root, which transformed her into Thorn. After killing her teacher, Professor Hollis, she reverted back to Rose. Rose returned to America and settled in Keystone City where Thorn headed a gang which harassed The Flash. When she was in control, Rose would approach Jay for help, claiming to be Thorn's sister.