In 2261, the Craters arrived at planet M-113. He began a multiyear archaeological excavation of the ruins of an ancient and extinct civilization. In the first four years of the excavation, there were heavy shipments of reports and artifacts from this excavation.
In 2265, Mrs. Crater was killed by the last of the M-113 creatures. Her husband buried her on a hill. He forgave the creature, who afterwards took on the appearance of his wife. After her death, there was a marked drop in shipments.
In 2266, when the USS Enterprise visited for a routine check, Crater was visibly upset and wanted them to leave. When it was discovered that a creature was killing them, James T. Kirk and Spock tried to apprehend him. He resorted to violence but was subdued. He explained about the salt creatures, equating them to the buffalo that were wiped out on Earth, and said that the creature was the last of its kind and deserved to live. Robert was eventually killed by the very creature he loved aboard the Enterprise. (TOS: "The Man Trap")