Lieutenant Kelowitz was a male Human Starfleet officer in the 23rd century. He served in the sciences division aboard the USS Enterprise in 2267 under the command of Captain James T. Kirk, during the historic five-year mission. He was one of the ship's tactical aides.
That same year, on stardate 2821, Kelowitz was the leader of landing party number two searching for the missing shuttlecraft Galileo, which had crashed on the planet Taurus II. His party was ambushed by the planet's inhabitants, resulting in one dead and two injured. He was later treated for his injuries in the sickbay. (TOS: "The Galileo Seven")
Later that year, on stardate 3045, Kelowitz was one of three tactical aides who beamed to the Earth observation outpost on Cestus III in 2267. Arriving, they discovered the colony had been destroyed by the Gorn, a previously unknown species. Captain Kirk ordered Kelowitz to flank the attackers. Of the three aides, he was the only one who survived the attack. (TOS: "Arena")
Kelowitz was part of the landing party to Omicron Ceti III on stardate 3417, and he was paired with Lieutenant Hikaru Sulu in investigating the mysterious colony there. It was Kelowitz who first noticed there were no animals on the planet. Later, he was taken over by alien spores, though the spores were eventually destroyed by a subsonic transmitter. (TOS: "This Side of Paradise")
Background information Edit
Kelowitz was played by Grant Woods.
The final draft script of "Arena" reveals that this character's role in that episode was at one point intended to have been filled by a new character named Molton, who the script describes as a "tactics officer". Likewise, in the script for "This Side of Paradise," the role Kelowitz fills was written for one Crewman Dimont. 
Many reference works referred to Kelowitz as a lieutenant commander, although he wore the braid of a full lieutenant in every appearance he made. He apparently was confused with Lang, who – despite wearing lieutenant commander stripes – was consistently called "Lieutenant Lang" in references. An actual inconsistency exists, however, in that Kelowitz wore a blue sciences division uniform despite being referred to as a tactical aide in "Arena". It seemed likely he could be a "generalist" officer who served between a few departments, as Kevin Riley, Kyle, and Leslie had been known to do, or simply that he served in a science section which performed a tactical function.
The novel A Choice of Catastrophes gives his first name as "Rogelio".