(Taken from the eponymous SG wikia article. Articles on Saiv concepts are normally my own work)
Saiv
Homeworld: Ravion
Language: Saiv
Average height: 1.8 metres (proletarian), 2.1 metres (aristocrat)
Skin color: Olive/tan
Hair color: Red, brown, black, amber
Distinctions: Carpal claws, carnassial molars, feline athleticism and sensory perception
Average unaltered lifespan: 97 terrestrial years (proletarian), 585 terrestrial years (aristocrat)
The Saiv are a sapient species originating from Ravion, one of the few with silicon-based biochemistries. They are the predominant species of the Saiv Empire, the youngest and smallest of the "big three" civilisations of known space. Other races tend to have violent encounters with the Saiv, or may be one of the races subjugated by the Empire, nurturing a discontempt for them.
Biology and appearance
Unlike other mammalian sapients, who evolved from primates, the Saiv evolved from mountain-dwelling felines. The skeleton is rounded and uniform, and large joints are shielded by silicon-fibre caps. Like their feline ancestors, the Saiv possess preternatural senses of flexibility, agility and balance, and proletarians are capable of prolonged physical exertion for up to 3 hours. In females, the upper molar regions of the mouth are each fused into carnassial molars, ending in fang-like canines, and both hands are clawed. In males, many feline characteristics are partially downplayed in favor of stamina and strength.
Due to filtration of Ravionic sunlight by the nearby Rodrighal "dust belt" in the Rahma system, Ravion experiences an extremely dark quasi-night during 23 hours of it's 33-hour rotation period and a twilight-like day during the remaining 10 hours. Like most life on the planet, the Saiv are naturally active during night and at rest during day. Saiv sensory perception and athleticism are drastically higher than humans during Ravionic night due to hormonal influence. The iris of the eye is microscopically porous, covering an inner layer that reflects light into the retina a second time, granting excellent night vision and illuminating the iris during ambient darkness.
Saiv externally appear almost completely human, a trait which remains unexplained.
Society and culture
Most Saiv live under the security of the Saiv Empire, a "quasi-democracy" in which the state strives to solidify the sentient rights of Saiv but power is obtained through political intrigue. Constituting a miniscule fraction of the Saiv species, the genetically superior "aristocracy" offshoot tends to occupy leadership roles. Saiv civilisation is perpetually gripped by low-level civil war to determine the occupant of the Eagle Throne, the symbol of supreme Imperial power, and will escalate if the incumbent Emperor shows signs of weakness.
History
Early History
Felis Hominid Sapiens first diverged from quasi-primates on Ravion around 550,000 years ago. Clockwork engineering was an early technology in Ravionic history, since the earliest analytical clockwork diagrams date circa. 10,000 B.C., during the iron age. Idols dating from the agricultural revolution circa. 8,000 B.C. seem to indicate that the emergence of the aristocrats coincided with the emergence of civilisation at this time. Civilisation of the next 8.5 millenia progressed through an ancient, medieval and clockwork age but no time period qualifies as a contemporary era.
Space Age
Isharo Cerillo united the planet's five nations in the 650s, forming the Saiv Empire. Ravion succeeded it's "bootstrap" space development in 662 A.D. when it entered the interstellar age, connecting various colonies formed earlier by a realspace exodus. The Saiv population on Ravion numbered slightly over 5 billion at this time. Soon, the Empire began subjugating neighbouring backwater worlds and toppling interstellar civilisations alongside further colonisation. By 2130 A.D., the Saiv sphere of influence measured 220 ly between it's two most distant points, and housed almost 20 billion Saiv and 5 subject species.
First Contact
Xin'Ta'Faxi
In 2030 A.D., a Xin'Ta'Faxi mining vessel began burrowing into an asteroid near the future Xin-Saiv neutral zone to acquire galathite ore. On the other side of the asteroid, a Saiv colony had recently been estabilished. The colony was shattered by the seismic activity resulting from the mining, casting all 67 inhabitants into space and subjecting them to explosive decompression. The mining vessel remained oblivious throughout the mining operation until a Saiv scouting vessel arrived to investigate lost contact with the colony.
The scout reported the "attack" to High Command back in the Empire. Rather than approach the unknown race with reconciliation and familiarisation, the Saiv Empire rashly launched a scout taskforce and warfleet in the direction of the aliens, with orders to engage on sight. The Saiv ships soon found the Korlaron system. The inhabitants of Korlaron reached out to the new species unaware of the asteroid incident, but their gesture was returned by siege cannon fire, turning millions into ash and silica. A contingent of Xin'Ta'Faxi warships had been kept on standby specifically for such an attack and immediately set a course for the Korlaron system to meet the aggressors. Though the agility and fluency of Saiv tactica nearly scattered the Xin contingent, the ruthless efficiency of the Xin ships could not be exhausted, sealing a victory for the Xin.
The Saiv warships promptly retreated to the Empire. Rather than try to seize the initiative, belligerents would analyse their telemetry and freeze colonisation in the direction of one another. The Xin'Ta'Faxi and Saiv would return to war 11 more times between 2030 and 2130 A.D., becoming disturbingly culturally acquainted by the final year.
Saiv in the interstellar community
Saiv are rarely interested in travelling outside the Empire, since they harbor an invariable disdain for other species. When they do, they might look for employment as bounty hunters but tend to become pirates and smugglers. Many races are distrusting of the Saiv and alliances between them and other races have never been long-lasting. Saiv respire in carbon monoxide and their eyes are sensitive to standard light levels, so they are seen wearing gas masks and (usually) shielding their eyes in some way.
By 2130 A.D., the Saiv were represented on Sraelvodakane by Sata Namrahn, the first permanent envoy commissioned by the Saiv Empire.
Sins Forums
However, when in a very dark environment, such as the moonless night side of Ravion, they are subject to massive hormonal influences and can actually turn animalistic. This hormone rush is also very exhausting. When the Saiv discovered fire, it alleviated the rush without having to visit the sleepy day side, creating the conditions for society and civilisation.