Aaron McCallum was a male Human who lived in the 24th century. In the 2370s, he held the rank of lieutenant in Starfleet and was assigned to the USS Defiant as a security officer. McCallum was aboard the Defiant during its historic exploration mission in the Gamma Quadrant in 2376.
McCallum accompanied an away team to Vanimel. Before going down to the planet, McCallum had a full body scan taken and a routine medical screening performed by the Yrythny before they allowed the team onto the planet. McCallum's retinal patterns were entered into a Yrythny database. Despite being accosted by several Yrythny, McCallum later accompanied Ezri Dax, Edgardo Juarez and John Candlewood on a tour of the planet Jeshoh was to give them. (DS9 novel: This Gray Spirit)