Crewman Darnell was a sciences division crewmember aboard the USS Enterprise in 2266.
In that year, Darnell accompanied Captain Kirk and Doctor McCoy to the surface of planet M-113, for the purpose of performing routine medical checks on Robert and Nancy Crater. While there, all three members of the landing party saw a different version of Nancy Crater, who was, in reality, a creature able to read the minds of its prey and project whatever image of itself that it wanted. The woman Darnell saw was a recreation of a beautiful woman he had once met on Wrigley's Pleasure Planet.
After successfully luring Darnell away, the creature killed him by extracting all of the salt from his body, leaving a series of red rings on his face where he had been attacked. The creature subsequently placed a borgia plant in his mouth, for the purpose of misdirecting the Enterprise crew into believing that he had died by consuming a poisonous substance.
He was the first person pronounced dead on-screen by Dr. McCoy.