The Hur'q were a race of aliens who invaded Qo'noS in the 14th century. When they were forced out, they took with them many Klingon treasures, including the Sword of Kahless. The word "Hur'q" later became the word for "outsider" in Klingonese.
In the aftermath of the invasion, the hero Ch'gran oversaw the construction of a fleet of seven starships using captured Hur'q facilities and technology. (ST - The Lost Era novel: The Art of the Impossible)
In 2372, a Vulcan geological survey team discovered a Hur'q ruins on a planet in the Gamma Quadrant and brought by a cloth that had been used to wrap the Sword of Kahless. Kor realised what the cloth was and had it authenticated by Jadzia Dax on Deep Space 9. (DS9 episode: "The Sword of Kahless")
Gothmara used Hur'q DNA to create a personal army, which she used to overthrow Martok in 2376. The Hur'q had huge heads, black eyes, long gray tongues and narrow lips. They had wide shoulders, bearing two arms with three fingers and two thumbs each. They average Hur'q stood a full meter taller than most Klingons. (DS9 - The Left Hand of Destiny novels: Book One, Book Two)
It was later discovered that the Hur'q were an ancient race of insectoid scavengers, whose physiology was based on that of army ants and the armor of the samurai, that plundered much of the galaxy before the majority of their race were trapped in another dimension. With most of their fleet lost, the Hur'q would eventually vanish but they did leave elite units of Kam'Jahtae warriors in stasis, to awaken at a time to bring the Hur'q civilization back to glory. They were defeated by the crew of the USS Typhon. (TNG video game: Invasion)