She is a Korean geneticist, and an ally of the Avengers. She was present at Stark Tower when the group returned from a successful mission, and put her medical expertise cellular regeneration to use patching a wound sustained by Clint Barton during the their campaign. She then grudgingly accepted an invitation to the Avengers' victory party when she learned that Thor was going to be there.
After most of the guests had gone home, Cho and the others were surprised late in the evening by the expected appearance of one of Tony Stark's Iron Legion robots. After admitting that it was the result of Stark's Ultron program, the robot attacked the group, and Cho could do little but run and hide while her battle-hardened friends fought back. In the following days, she returned to her work in South Korea as the Avengers set off around the globe trying to deal with their new robot problem.
Cho was dragged helplessly back into the conflict when Ultron arrived at the U-Gin Genetics Research Facility in Seoul where she was working. The robot needed her expertise with cellular regeneration, and her regeneration cradle, in order to construct a new body for himself, and to that end he bound her to his will with Loki's Sceptre. Once enthralled, Cho complied with Ultron's edicts and constructed a complete android body for him, but during his personality transfer into the new form, Wanda Maximoff saw for the first time what his true intentions were and used her power to end Cho's enslavement. Cho discretely overrode the transfer while Ultron was occupied with Wanda, and was rewarded for her action with an energy blast from the enraged robot. She survived the attack however, and was able to relate what had happened to Steve Rogers when he arrived.
She is portrayed by Claudia Kim.