"Kate Wilson" was the assumed identity of a member of the Committee, an organisation of aliens that took over planets. She was adopted by journalist George Wilson, and had to pretend to be a normal human. When he started writing conspiracy theory books, she gave him ideas that were actually real facts about the Committee. His books became wildly popular and she worked as his agent.
Meanwhile, she became a YouTube star by making videos discrediting his theories. When Sam Hallett started investigating Jack Harkness and Torchwood, Kate killed him and made his death look like a suicide. Jack realised Kate's identity and came to her hotel room, but she shot him, severing his spinal cord. While Jack was dying, she explained her role in her father's success, then shot him too. She left, leaving Jack to be found by the police. Jack came back to life and escaped. (AUDIO: The Conspiracy)