Jotuns
The metaspecies known as the Jotuns were the first extraterrestrials encountered by humans. Jotuns are an ancient race of immense interstellar cyborgs found in many small colonies throughout the Milky Way Galaxy. They are both powerful and bellicose, given to initiating conflict both between themselves and others.
Jotuns were first detected by Galliman in 2110 CE using the first generation of hyperspatial observation equipment, shortly before the first direct images of extraterrestrials were recorded in 2120 CE by a research probe sent to the star Pollux at a distance of 34 light years from Earth, where a group of Jotuns were encamped for several centuries. This encounter followed the discoveries of various alien artifacts throughout the Sol System, and led to widespread panic and psychological trauma for human beings. This hysteria was at least partly caused by the fact that Jotuns were obviously cybernetic organisms rather than biological. The Outlook War was in full career by this point, and the speculation at the time ranged all the way to belief that Jotuns would enter the war on the side of the Progressivists.
It was this turmoil that prompted Old Earth governments to back the infamous Belt Exploration and Industrialization Consortium (BEIC) in mounting the first Interstellar Age expedition to the Jotun colony and then establish a trading outpost in orbit around Tyndareus, a large gas giant that orbits Pollux. BEIC was successful in making contact (of sorts) with the Jotuns, and even trading with them over time, but the aliens were so far advanced beyond human beings technologically and psychologically that it took centuries to develop any real rapport and understanding between the two species. The polycameralism of Jotun brains was eventually emulated by Naotians and some Peretians, leading to a deeper appreciation of Jotun culture, but this development lay centuries in the future.
The Thannic Colonizers were famously attacked by a group of Jotuns 52 light years from Earth around the star Castor. The outcome of the conflict was indeterminate, and an uneasy peace between Humankind and the Jotuns ensued. There have been sporadic conflicts with individual Jotuns over the centuries, especially in encounters with the Xenocorps in the Frontier and Periphery, but no widespread warfare.