Elim Garak was a Cardassian tailor on Deep Space 9. He was an exiled ex-operative of the Cardassian Obsidian Order.

He was the protégé of his father, Enabran Tain, head of the Obsidian Order though their relationship was kept secret. Garak was instrumental in the arrest and execution of Gul Dukat's father.
(DS9: "The Wire", "For the Cause")

As an Obsidian Order operative, Garak volunteered to have a cranial implant installed in his skull which would help him resist torture.
(DS9: "The Wire")

Garak could speak Klingon
(DS9: "The Way of the Warrior")

In 2368, Garak somehow betrayed Tain, and Tain ordered him killed. Garak escaped, but was exiled from his homeworld of Cardassia Prime.

He gave many reasons for his exile to Dr. Bashir none the truth for as Garak was fond of saying, "The truth is usually just an excuse for lack of imagination." He once claimed that all I say is true - "especially the lies".
(DS9: "The Wire")

When Sisko asked Garak if the attempted assassination plot against him in 2371 was somehow related to his exile, he stated that he seriously doubted that the finance ministry would try to kill him for not paying his taxes.
(DS9: "Improbable Cause")

After his exile, Garak took up residence aboard Terok Nor, under the command of Gul Dukat. Bitter over Garak's involvement in his father's death, Dukat attempted to have Garak executed.
(DS9: "Civil Defense")

Garak again escaped death's grip, surviving to see the Cardassian government withdraw from the station in 2369. He set up a tailor's shop, and went into business soon after his fellow Cardassians left the station.
(DS9: "Past Prologue")

Garak kept contacts in the Cardassian Union after his exile, and when Starfleet took control of Deep Space 9, he attempted on occasion to use his position as the only Cardassian still aboard to regain his usefulness.
(DS9: "Profit and Loss")

Bashir and Garak began to have weekly lunches, where they grew to be friends.
(DS9: "Cardassians")

Garak helped uncover Tahna Los' real intentions after he was granted asylum by Sisko.
(DS9: "Past Prologue")

He helped foiled a plot by Dukat to embarrass a Cardassian diplomat who opposed Dukat.
(DS9: "Cardassians")

In 2370, Garak was offered a chance to regain his position on Cardassia by killing members of the Cardassian Underground.
(DS9: "Profit and Loss")

Garak was not part of the crew that entered the Gamma Quadrant in search of the Dominion.
(DS9: "The Search, Part II")

In 2371, an explosion destroyed Garak's shop.
(DS9: "Improbable Cause")

Garak joined Tain on a joint Obsidian Order-Tal Shiar mission to destroy the Founders' homeworld.
(DS9: "The Die is Cast")

Garak contacted Gul Dukat in 2372 to warn him of the impending Klingon invasion of Cardassia.
(DS9: "The Way of the Warrior")

Garak would later admit, however, that he was tempted to shoot Dukat in the back during the conflict but decided against it.
(DS9: "Call to Arms")

When Dukat's half-Bajoran daughter, Tora Ziyal, came to the station in 2373, Ziyal became attracted to Garak.
(DS9: "For the Cause")

In hopes of finding any survivors of the Cardassian fleet, Garak returned to the Gamma Quadrant on the Defiant in 2372.
(DS9: "Broken Link")

On his deathbed, Tain finally admitted that Garak was his son, and told Garak that he was proud of him.
(DS9: "By Inferno's Light")

He joined a mission to station Empok Nor to find parts to repair Deep Space 9.
(DS9: "Empok Nor")

When Starfleet withdrew from the Bajoran sector at the start of the Dominion War, Garak joined the crew of the USS Defiant.
(DS9: "Call to Arms")

He was part of Sisko's crew that destroyed a Ketracel-white facility.
(DS9: "A Time to Stand", "Rocks and Shoals")

His knowledge of the Cardassians proved a valuable asset to Starfleet Intelligence.
(DS9: "Favor the Bold")

When Starfleet retook Deep Space 9 during Operation Return, Garak found that Ziyal had been killed by Damar.
(DS9: "Sacrifice of Angels")

Later in 2374, Captain Benjamin Sisko asked for Garak's help in finding evidence that the Dominion was planning an invasion of Romulus.
(DS9: "In the Pale Moonlight")

Garak spent the rest of the war he excelled at decoding Cardassian transmissions for Starfleet Intelligence.
(DS9: "Afterimage")

During the final months of the war, Garak used his contacts in the Cardassian Union to find the leader of the Cardassian Liberation Front, Damar.
(DS9: "When It Rains...")

After Mila was killed in the final days of the Dominion War, Garak joined the uprising and participated in the storming of Dominion Headquarters.
(DS9: "What You Leave Behind")