The Yuuzhan Vong
The Yuukhan Vong are an extra-galactic humanoid species that invaded the galaxy, nearly wiping out the Republic and its neighbors in a war waged from 25 ABY until 29 ABY, though they had a presence in the galaxy to various degrees as far back as the Mandalorian Wars some 4,000 years ago. The war was responsible for the deaths of hundreds of trillions of sentients across the galaxy, a fact that fuels anti-Vong sentiments galaxy-wide to this day. However, in the aftermath of the war, the Yuuzhan Vong surrender required that they disarm and withdraw from the worlds they had conquered. Today, all members of the species now reside on the sentient world of Zonama Sekot, a planet capable of hyperspace travel that began as the seed of the original Yuuzhan Vong homeworld in their former galaxy. Zonama Sekot has withdrawn to an undisclosed location in the Unknown Regions while Vong society rebuilds.
Little certain knowledge of their origins survives, and their culture in the ages leading up to their invasion is only partly understood by outsiders, though it was known to be caste-driven and heavily religious. The Yuuzhan Vong’s most distinctive trait was their virulent hatred of inorganic technology—all of their own technology is centered around genetically engineered life forms. They were also known to glorify pain, and it was common practice for them to modify their bodies with symbiotic life forms designed to replace their own organs and body parts and grant them extra capabilities. How many of these features remain, and in what form, is not widely known today as their society has remained isolated from those of their adopted galaxy since the end of the war.