From Gineipaedia, the Legend of Galactic Heroes wiki
The Space Pirates were not a single organization, but rather a disorganized entity consisting of various independent pirate ships and groups that preyed upon the Frontier Worlds of the Galactic Federation in the third century UC. The Pirate Wars began in 206 UC (3006 CE) when the Galactic Federation created the Federation Armada to combat the Space Pirates. Within 2 years, the Federation was successful in severely crippling the Space Pirate threat. The two admirals who led the Federation Armada to victory, Michel Cuffren and Christpher Wood, were hailed as heroes.
Despite the war, however, interstellar piracy would continue to plague the remote frontier regions until as late as 288 UC (3088 CE), when a particularly notorious pirate band, the Main Street Pirates, were defeated by Rudolf von Goldenbaum. (LOGH: 'Julian's Journey, Mankind's Journey')