Axum was a Borg drone with the designation Five of Twelve, Secondary Adjunct of Trimatrix 942. He was one of several drones who experienced Unimatrix Zero while regenerating. This dream state allowed the drones to experience individuality, and resume their former identities. He carried on a six year romance with Annika Hansen in Unimatrix Zero.
Three years after Hansen escaped the Borg as Seven of Nine, he contacted her to help save Unimatrix Zero. The drones had manufactured a nanovirus that could hide the dream state from the Borg Queen, so she could not sever the link in Unimatrix Zero. Axum needed someone in the real world to release it into the Borg Collective.
However, the USS Voyager crew devised a plan to grant the drones of Unimatrix Zero their individuality and allow them to retain their memories while conscious as drones in order to begin a resistance movement against the hive. The plan worked and Axum became a leader of the resistance movement, trying to enlist the help of Species 8472 near fluidic space in the Beta Quadrant. However, Voyager was too far from Axum's physical location and he and Seven were forced to separate once again. (VOY: "Unimatrix Zero", "Unimatrix Zero, Part II")