The Starfleet engineer on AR-558 who works with Ezri Dax to turn the Dominion's Houdini mines against the Jem'Hadar.
Kellin is the engineer of the battered Starfleet garrison on AR-558 in The Siege of AR-558. He is worn down by months of fighting and by the Houdini mines, which phase in and out of subspace and kill soldiers without warning.
Working with Ezri Dax, Kellin finds a way to make the Houdinis visible so they can be moved out of the camp and used against the advancing Jem'Hadar, helping the garrison hold the relay. He was played by Bill Mumy.