Emblem of the Klingon Empire
Ch'gran was a great Klingon warrior who lived approximately a thousand years ago. In the wake of the Hur'q invasion and looting of Qo'noS, Ch'gran rose to prominence by urging the Klingon people to take to the stars and conquer all threats to the Klingon people before they suffered another invasion. Using captured Hur'q facilities and technology, Ch'gran oversaw the construction of a fleet of mighty warships, numbering seven in total, and on the anniversary of the Hur'q invasion, Ch'gran and the fleet ventured forth into space. The fleet later sent word that they had located a world on which to plant their flag, but were never heard from again.
The mystery surrounding Ch'gran's fate, and that of his fleet, was later solved when, during the 2290s, one of Ch'gran's ships was found adrift in the Betreka Nebula, and again in 2328, which was found by the Cardassian's on Raknal V. When the Cardassians refused to surrender the derelict, the Klingons lead multiple incursions into the Raknal system, starting the long-remembered Betreka Nebula Incident.
The fleet's last word was that they'd found a world on which to plant their flag, and then they were never heard from again. In the 2290s, one ship was found adrift in the Betreka Nebula. In 2328, the wreckage of another was found by the Cardassians on Raknal V.
Klingon Imperial Intelligence discovered information on the ship found in the Betreka Nebula that revealed the fleet's fate: Ch'gran's real intention for his fleet, was not to provide security for the Klingon's people's future by conquering other worlds, but instead conquer them for himself, and after building a larger fighting force, return to the homeworld and take control, putting himself at the top of a new Klingon Empire. Ch'gran's subordinate Captains, not wanting a dictator in power, mutined and rebelled to stop Ch'gran, and the fleet destroyed eachother, killing Ch'gran and ending the threat he posed.
The Intelligence official who discovered the information, a descendant of Ch'gran's House, sealed the information, but was nevertheless revealed to certain members of the nobility, including Chancellor K'mpec, who officially changed the Empire's position on the Raknal V wreckage due to the possible information it contained, ending the Incident, but kept the information from the Klingon people to preserve Ch'gran's memory. (TLE novel The Art of the Impossible)