Agent X19 was a spy for Dr Robotnik in the later days of RBR.
In her only appearance in Sonic the Comic, she was sent to the Special Zone to gather intelligence on whether the zone was fit for invasion. Unfortunately for her, she found herself being attacked by Mister Shifter in New Tek City and would have been shot dead, had Sonic the Hedgehog not arrived just in time to catch the bullet. While Sonic battled the shapeshifter, Agent X19 quietly slipped away to return to Citadel Robotnik, where she reported to her master that the Special Zone forces were too powerful for an invasion to work, but Robotnik would never guess who she met in New Tek City.
She has not been seen since.