Star Trek: Voyager: Season 2, Episode 24

2 - 24: Tuvix

Stardate: 49655.2 While returning from an away mission, a transporter accident merges Tuvok and Neelix into one new being with the personality of both combined. He calls himself "Tuvix." But the  Doctor's search for how to restore their original forms causes a moral dilemma as Tuvix does not wish to be terminated.