Gul Dukat (Marc Alaimo) hated Star Trek: Deep Space Nine's Cardassian tailor, and former spy, Elim Garak (Andrew J Robinson) with a passion, and the feeling was mutual. Garak was exiled from Cardassia Prime and forced to live on Terok Nor. He remained on the station after it was passed into Federation hands and renamed Deep Space Nine, where he formed a close bond with Dr. Julian Bashir (Alexander Siddig) and continued to be a thorn in the side of Terok Nor's former prefect, Gul Dukat.
In Star Trek: Deep Space Nine's early days, Gul Dukat and Elim Garak had a strong dislike of each other, for reasons that weren't made immediately clear. It appeared to stem from the conflict between the Cardassian military and the secretive intelligence agency the Obsidian Order, of which Garak was a member. However, it wasn't until Star Trek: DS9 season 4 that the origin of Dukat and Garak's feud was revealed, and further complicated by the arrival of Dukat's daughter Tora Ziyal (Melanie Smith).
