- You may be looking for Three (The Abandoned).
When the Ark arrived at Refusis II, Three talked with One about what should be done with the Ark's humans. One told Three he had hidden a fission bomb on the ship to kill the humans once the Monoids were settled on Refusis. Three also warned One that he believed that Four was planning a mutiny. Three was correct and was killed during Four's mutiny. (TV: The Ark)