From Gineipaedia, the Legend of Galactic Heroes wiki
Carle Palmgren was born in 2664 on the colony world of Rondolina, in the Sirius starzone. Little is known of Palmgren's early life, but when the United Earth Government invaded Rondolina in 2689 CE, Palmgren, then a 25 year old man working as a broadcast reporter, was subjected to a random inspection by the occupying Space Force army. Palmgren refused the search, and was badly beaten to the point of unconsciousness.
When Palmgren recovered, he found himself sprawled atop a pile of human corpses, doused in rocket fuel and set on fire. Thanks the the thick black smoke of burning human flesh, Palmgren was able to escape from the scene unnoticed.(LOGH: 'To Earth')
Some time following the Bloody Night massacre, Carle Palmgren joined the Anti-Earth Movement, and quickly became one of the movement's leaders. He followed the Sirius Revolutionary Congress to Prosperina, a colony world in the Proxima Starzone, where he first met Winslow Kennes Townshent, Joliot Frankul and Chao Yuiling. The four men quickly became the leaders of the Anti-Earth Movement, and reshaped the loose alliance of colony worlds into a centralized military organization: the Black Fleet. Palmegren's natural charisma made him the perfect candidate for the Black Fleet's leader, and he spent much of the Earth–Sirius War coordinating between the Black Fleet and the Sirius Revolutionary Congress. Frankul became the military commander of the Black Fleet; Townshent oversaw logistical and supply matters; Chao became the Fleet's Director of Covert Affairs, initiating various acts of sabotage and espionage against the United Earth Government.
It is unknown whether or not Palmgren was present in any of the major battles of the Earth–Sirius War, the liberation of Rondolina, or the Second Battle of Vega, but given his position it is likely he would have been present for the final battle of the war, the Battle of Sol in 2704 CE. At the Battle of Sol, the Space Force of the United Earth Government was finally defeated, and the Black Fleet bombarded Earth's surface, an act resulting in billions of civilian casualties and one of the greatest war crimes in human history.(LOGH: 'To Earth')
With Earth effectively destroyed, the colony worlds of the Galaxy were only loosely united thanks to their cooperation in the Sirius Revolutionary Congress of the Anti-Earth Movement. A charismatic hero, Palmgen was able to mold the Revolutionary Congress into a stable government, backed by the power of the Black Fleet, encompassing all of the colony worlds. This new galactic government was called the Sirius Republic.
Unfortunately, the Sirius Republic was too dependent on the military power of the Black Fleet. Palmgren likely intended to decrease the power of the fleet and increase the centralized authority of the Republic's congress, but died too early to realize his dream. Carle Palmgren was struck down by a heart attack in 2706 CE. On his deathbed, he lamented the fact that he had been unable to finish building his republic. Seeming to realize the inevitability of the republic's collapse, Palmgren left the world commenting that if he had only had five more years of life, he could have finished building his new republic.
After Palmgren's death, the Sirius Republic fractures as various officers of the Black Fleet attempted to seize power for themselves, leading to more than three centuries of disorganized chaos in the galaxy. (LOGH: 'To Earth')