Doctor Prospect is a scientist for Foundation X heading their project to create Quarks and the main antagonist of the movie Kamen Rider W Returns: Kamen Rider Eternal.
Prospect headed Foundation X's research into Quarks, kidnapping people from across the world and forcibly converting them into Quarks as well as killing the weaker Quarks through use of the Heaven's Horn barrier.
However, Mina, a Quark Prospect had experimented on, betrayed him and teamed up with Katsumi Daido and NEVER to free the other Quarks. Using his Eyes Gaia Memory, Prospect transformed into the Eyes Dopant to face Katsumi as Kamen Rider Eternal. Prospect used his Dopant powers to kill all of the Quarks (though Mina survived unbeknownst to them), causing Katsumi to go crazy from witnessing their deaths. Eternal then defeated Prospect by using his Maximum Drive to destroy the Eyes Memory, causing Prospect to fall victim to its psychic-killing effect.