Nyssa al Ghul (Gotham)

"Gordon: This is James Gordon. Who am I speaking to? Walker: A friend who wants you to know you have allies across the river. We will find a way to help you."

- Walker responding to Gordon's message.

Theresa Walker is one of the main antagonists in the fifth and final season of the FOX TV series, Gotham. She is a rogue government agent who brainwashed Edward Nygma into massacring the Haven and sending Eduardo Dorrance to enact her own mysterious agenda for the city.

She is portrayed by Jaime Murray.

Biography
Following Ra's al Ghul and Jeremiah Valeska's actions of turning Gotham City into a No Man's Land, Theresa had Hugo Strange brainwash and revive Edward Nygma to do her bidding.

When Wayne Enterprises sends a chopper to the city with supplies, Theresa uses Edward to shoot the chopper down with a rocket launcher. Later, she responds to Jim Gordon’s message, saying that she has help on its way to him. She later has Nygma fire an RPG at the Haven, blowing it up and killing everybody inside.

Walker then sends Eduardo Dorrance and his Delta Force to hunt down Nygma and have Gordon kill him to ensure his loyalty, Unfortunately, Gordon refuses and escapes, forcing Dorrance to have Nygma kill him.