A Federation archaeologist working on M-113 who shelters the shapeshifting creature that has taken the form of his late wife Nancy.
Professor Robert Crater spends years excavating the ruins of a vanished civilization on M-113 with his wife Nancy. In The Man Trap the Enterprise arrives for a routine medical check, and Crater's guarded, irritable manner hints that he is hiding something. The truth is that Nancy is long dead, killed by the planet's last surviving native creature, a salt-hungry shapeshifter that now wears her face.
Crater protects the creature out of loneliness and a sense that it, like the buffalo, is the last of its kind, supplying it with salt in exchange for companionship. His loyalty costs lives aboard the Enterprise, and he is killed before the creature is finally stopped. He was played by Alfred Ryder.