The last known member of a species native to planet M-113, a telepathic predator that drained salt from its victims while disguising itself as people they knew.
The M-113 creature was the final survivor of a dying race on the planet M-113. It needed salt to live and killed by drawing every trace of it out of a victim's body. It could cloud minds telepathically, appearing to each observer as someone familiar or desirable.
In The Man Trap, it had killed the archaeologist Nancy Crater and taken her place, sheltered by her husband Robert Crater. Aboard the Enterprise it murdered several crewmen while posing as different people. McCoy, who still saw it as Nancy, finally fired on it as it attacked Kirk, and it died in its true form.