A smooth-talking, self-professed "plain and simple tailor" was DS9's lone Cardassian resident, exiled there upon Starfleet's arrival and eventually confirmed after much circumlocution as a former Obsidian Order spy and son of its onetime leader, Enabran Tain. Garak's own clouded history as an OO agent, coupled with the typical Cardassian penchant for convoluted intrigue, often put him at odds with some of his own people, including agent Corbin Entek and Gul Toran, whom he killed on the spot, and Gul Dukat, whose father he had tortured and killed years before.
Garak was exiled after being forced even to betray his father/mentor, and they parted bitterly. In fact, Tain refused to give his son any forgiveness when he died alongside Garak in a Dominion prison camp in 2373. Two years earlier, Tain's planned return to power led to a failed assassination attempt on Garak, but the tailor had his shop blown up to focus attention on the Flaxian sent to kill him; Garak was the only one of five targets with data harmful to Tain to survive. A year earlier, Garak had nearly died when the pain-blocking device he was implanted with broke down two years after he'd grown addicted to the full flow of endorphins he decided to release.
On DS9, where his quarters were Chamber 901 on Habitat Level H-3, he struck up an early friendship with the young Dr. Bashir, and later came to respect Odo as well, especially after their witnessing of Tain's disastrous Cardassian-Romulan debacle against the Founders Homeworld in 2371. His rage over being dismissed by the Female Changeling led to his abortive plan to bomb their new homeworld with the U.S.S. Defiant, but the act drew a six-month sentence from Sisko; later, he would help free twinned prisoners from his father's Dominion prison camp despite his claustrophobia. Ironically, he became enamored of Dukat's half-Bajoran daughter Tora Ziyal in 2372 during her stay on DS9, after he decided he could trust her with a rare show of vulnerability, much to both Kira and Dukat's annoyance. And, despite his exile, he still has friends on Cardassia who relay information. He had hoped to end his exile with acts of valor, but Dukat's prominence at every turn of events has hampered that. Garak knows fluent Klingon, spent over a year as the "gardener" of the Cardassian Embassy on Romulus during a year of many Romulans' mysterious deaths, and dislikes hand-to-hand fighting.
Garak's participation in the Cardassian underground was crucial to the defeat of the Dominion in 2375. He was finally able to return to his homeworld at that time, but sadly it lay in ruins after the Dominion campaign of terror against his people.