|Family|| Declan Gage (father)|
|First Appearance||"Blind Spot"|
|Last Appearance||"Frame" (mentioned)|
Jo Gage was the biological daughter of Declan Gage and an unknown woman, who committed suicide when Jo was seven.
Apparently, her father neglected her because she was not the son he wanted. That´s why she let him teach her all about serial killers to be near him. Still he never taught her about boys or anything else and surrounded her with serial killer profiles and their crimes. He also believed there could be no female serial killers.
She proved him wrong, by killing three girls, and by a murder attempt on Eames, and then tried to blame it all on her father to get his attention once and for all. She confesses to Det. Robert Goren and is subsequently arrested. This event also broke Goren´s relationship with Declan.
She is mentioned again in Frame. She was sent to an asylum, where she bit off her tongue, because she could not stand to see her father again. As a result of this, she slipped into a coma.
The event pushed her father over the edge and turned him into a killer.