Jonathan Cartwright (Arrowverse)

Johnathan Cartwright (also known as Mouse) is a secondary antagonist in the first season of Batwoman.

History
Johnathan Cartwright grew up in isolation due to his disfigurement. He lived alone with his father until they saved Beth Kane. Johnathan’s father held Beth against her will and during that time, Johnathan befriended her. At some point, he was sent to Arkham Asylum and Beth became the criminal Alice. Johnathan (going only by Mouse) escapes Arkham and rejoined Alice as they hid out in an abandoned apartment.

Alice and Mouse conspired to steal a weapon from the company ran by Alice‘s stepmother, but mistrust formed between the two of them when Mouse found out Alice had been hiding that her sister Kate Kane was Batwoman. Mouse raged at Alice for deception and affection for Kate, causing him to use the acquired weapon to kill their hostage.

Alice later talked with Mouse and said she wanted both Kate and Mouse to be with her. Mouse said he doesn’t like to share and Alice told Mouse that they would be sharing Kate, assuring Mouse they would kill Kate if she didn’t join them.