Daniel Arbor was a gunnery sergeant in the Systems Alliance Navy. He served for most of his career on the Systems Alliance frigate known as the SSV Midway, under the command of the widely-renowned Captain Nick Salvatore. Arbor fought alongside Captain Salvatore on numerous occasions, and participated in the rescue mission to the surface of the colony planet Mindoir, a small agricultural-based human colony in the Attican Traverse, a region of space bordering the largely lawless Terminus Systems. During the rescue mission, Arbor, Salvatore, and the rest of their team rescued Johun Shepard, a future member of their crew and Spectre, the elite agents who enforced the will of the Citadel Council throughout the galaxy.
Gunnery Sergeant Arbor later served alongside Johun Shepard and his friend Nigel O'Conner, after they were assigned to serve alongside him on the SSV Midway. While patrolling the Terminus Systems for signs of batarian pirates and slavers, Arbor taught Johun Shepard and Nigel O'Conner how to operate a Mako, a light tank and rover for planetary surface exploration, on the remote, desert world of Edolus.