Jack Brennan

Jack Brennan is a fictional character in Larry Niven's Known Space universe, from the novel Protector. Jack Brennan was a smuggler who lived in the Asteroid belt in Sol system. He found an artifact in Uranus's trailing trojan point and was on his way to Earth's Moon to sell the artifact. Brennan was kidnapped by Phssthpok the Pak Protector and was left in confinement near Tree-of-Life root. After eating the root, he transformed into the Pak Protector stage of human. As a Human Protector, he steals Pssthpok's ship and sets off for Alpha Centauri. From the point of view of Flatlanders, he makes a pit stop in the far reaches of the solar system, and then continues his journey. In reality, he had constructed a base called Kobold and began his watch on humanity. He "samples" humans every decade, alternating from the belt and from Earth. He abducts them for a few months and sends them back with no memory of the encounter, except for the advisement that the time is missing from their lives... full article at wikipedia