Gavril

 was a Tractite.

When the Earth Empire purged Tractis after a rebellion, Gavril was one of the survivors who escaped. Acquiring a Time Tree, they travelled back to Earth's prehistory to prevent humans from ever evolving. Gavril was lost along the way and wound up in the 20th century. He had been infected with the disease that was intended to wipe out humanity and tried to carry out that mission. He was stopped before he could release it. (PROSE: Genocide)