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 a team to Vanìmel. 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 McCallum later accompanied Ezri Dax, Juarez and John Candlewood on a tour of the planet Jeshoh was to give them. (DS9 novel: This Gray Spirit)

Several weeks later, McCallum responded to an alert after the D'Naali nicknamed Sacagawea by the crew became distressed. (DS9 novel: Cathedral)