Borum was a Bajoran. During the Occupation of Bajor he was imprisoned on Cardassia IV. He remained there even after the Occupation ended. He was held, along with his close friend Li Nalas, at the Hutet labor camp.
In 2370, he convinced a Cardassian maintenance worker into giving Li's earring to Rionoj, who made a promise she would deliver it to Bajor. Being unable to get to Bajor, she delivered the earring to Quark on Deep Space 9, who then gave it to Kira Nerys. This let her know that Li was still alive.
After Kira and Miles O'Brien arrived to save Li, they could not take all the prisoners with them. Borum was adamant that Li make it back to Bajor, to which Kira gave her word. Borum and a few others stayed behind, to stop the pursuing Cardassians and ensure Li made it back to Bajor. After Li's safe return, the Cardassians claimed the imprisonment of the Bajorans had not been authorized, and Borum and the remaining prisoners were returned to Bajor. (DS9: "The Homecoming")