Helen Clay was a Professor at the University of New Earth. In the year 5,000,000,012, she created the Testimony Foundation, which used time travel technology to preserve the memories of people from the past. Her face was used for the default appearance of Testimony’s glass avatars.
Information about Clay was contained within the Dalek Pathweb, which the Twelfth Doctor accessed through Rusty to learn her identity. (Twice Upon a Time)