After much speculation, Overwatch revealed Orisa as the 24th hero in the game. She has been on the Public Test Realm for the past two weeks, and will officially be making her debut on the live servers on March 21.
Orisa was designed by child genius Efi Oladele as a replacement defense bot for the OR15 units that got Doomfisted at the Numbani airport prior to Orisa's unveiling. Game Director Jeff Kaplan says the new Omnic is an "anchor tank," designed to stand its ground against heavy fire. Blizzard released a behind-the-scenes video showing the thought the went into the art and the animation of the new character. Think of a Gothic Zarya with Bastion's cannon. "It was instantly fun," Kaplan said.
An interesting point made in the video is that Orisa is joining Overwatch in her infancy. She really does not have a lot of backstory on her own, other than Efi. While other characters have a history, Blizzard will be able to evolve Orisa as the game progresses. This could really come into play as her AI develops over time, opening up plenty of new story angles.