"I can't think of higher praise."
Kellin served during the Dominion War in 2375. He was assigned to AR-558, a planet that the Federation Alliance had captured from the Dominion, under the command of Captain Loomis. They were assigned to protect the planet's communication array. Other members of the 150-person unit included Commander Parker, Vargas, Reese, McGreevey, and Lieutenant Nadia Larkin.
The team successfully held the location for five months, despite expecting to be replaced in ninety days. Over a hundred of the unit were killed over this time, including Loomis and Parker. Kellin worked to understand the Dominion technology in the communications array in order to use it, though he had little success.
When Captain Benjamin Sisko and his crew arrived to help the unit, Ezri Dax helped Kellin with the array. Sisko ordered them to pause and switch to expose the subspace anti-personnel mines (known as "Houdinis") that had threatened them, and to turn them on the Jem'Hadar. In the process, Dax and Kellin became friends and he was impressed with the engineering knowledge she had.
Kellin was played by Babylon 5 and Lost in Space star Bill Mumy. The actor had wanted to appear on Star Trek: Deep Space Nine ever since the show's first season, and was offered many alien roles, but didn't want to wear extensive prosthetics. (Star Trek: Deep Space Nine Companion (p. 626))