Robert Johnson was a Human male born in 2238, who was married to Elaine Johnson. During the 2260s, he was the leader of the scientific expedition at the experimental colony on Gamma Hydra IV.
When the planet went through the trail of a comet in 2267, radiation hit the planet, causing all of the colonists to age rapidly and subsequently die of old age. Johnson survived until the arrival of the USS Enterprise and met the landing party along with his wife.
He was brought to sickbay, but died soon afterwards. (TOS: "The Deadly Years")