Brun was once an associate of Enabran Tain, the former head of the Cardassian Obsidian Order. Tain believed that Brun could not be trusted.
On Tain's deathbed in 2373, Elim Garak assured him that Brun had been "taken care of". (DS9: "In Purgatory's Shadow")
This character was only mentioned in dialogue.