Bio: During a robbery at S.T.A.R. Labs, Rudy Jones was in an
accident that turned him into a human parasite. One touch of the
Parasite's hands will leave a victim weakened and prolonged contact will
kill them. When he drains his prey, Parasite not only takes on that
person's energy, but their knowledge, memories, and any skills or powers
they might have. He joined the Secret Society to destroy Superman, who
he blames for the accident.
For more, refer to the Justice League Unlimited bio.