Sergyar
Sergyar is one of the three planets that comprise the Barrayaran Empire in the Vorkosigan Saga. The other planets are Barrayar and Komarr. The entire planet has been said to be the personal property of Barrayaran Emperor Gregor Vorbarra.
Discovery
Sergyar was first discovered by Barrayar shortly before the Escobar War. It is the site where Cordelia Naismith and Lord Admiral Aral Vorkosigan first met when her Betan Astronomical Survey ship landed a party to explore and catalogue the planet and its biome, unaware of Barrayar's earlier territorial claims on the planet.
Strategic importance
Sergyar is strategically important because it is a link from Komarr to Escobar, and then Beta Colony. This opens up trade in the wormhole nexus significantly for Barrayar. It was the site of massive caches of ordnance and other materiel for Barrayar's abortive attempt to invade and conquer Escobar.
Native life
Native life on Sergyar seems to have a general radial symmetry, with most lifeforms having six limbs or appendages. While there are no known native sentient life forms, there is a diverse ecology. Various species mentioned include large predators referred to as 'fuzzy crabs' that hunt in packs, and their 'hexapedal' herbivorous prey - large, six-footed grazing animals.
Smaller creatures, radial in design, seem to fill the ecological niches filled by insects on Earth. There are also mentions of airborne lifeforms, similar in appearance to jellyfish, that float through the atmosphere, supported by gas-filled sacs, that descend from above to leech blood from larger, moribund lifeforms. The gas is mostly hydrogen, and will explode if exposed to fire.
In later books, there are mentions of a Worm Plague on Sergyar; its survivors have puckered, swirling scars on their skin.
Name
According to the naming scheme of Barrayar, the particle "-yar" likely means "planet", "world" or something similar. Thus, Sergyar was named for Crown Prince Serg, the one-time heir apparent to Emperor Ezar Vorbarra and father of now Emperor Gregor Vorbarra. Prince Serg died in the Escobar War.
Government
The seat of its government was originally a settlement dubbed "Chaos Colony." In the later series, Count Aral and Countess Cordelia Vorkosigan governed Sergyar as Viceroy and Vicereine, respectively. A steady flow of immigrants from Barrayar and Komarr made new homes on Sergyar, many of whom were former residents of the Vorkosigan District.
In the latest books, Sergyar is now the home to over 2 million émigrés, from Komarr, Barayar and even technical experts from Beta Colony, who were recruited by the Vicereine and elected to make new homes on Sergyar. Sergyaran society continues to develop, with a lifestyle commensurate with Galactic standards in medicine, communication etc. There is a movement afoot to transplant the government to the thriving city Kareenburg, more hospitably located in a wet, temperate region, as Chaos Colony was is essentially the overgrown offshoot of the original military landing site, chosen for its access to caves to hide military equipment, and for no other real purpose. There are also plans to establish a major military and transportation enclave, complete with new spaceport, in a sizable town named Gridgrad, which would further diminish Chaos Colony as a civic and political center.