The First Gigaquadrant is believed to have harboured millions of civilizations in its 13.7 billion years of history. Life itself, from evolution or creation to its ultimate destruction is one of the fastest processes the history of the universe. Many civilizations go out in a flash, or revert to primitivism during its planetary history, indeed the universe is populated by various ruined planets, heavily polluted or irradiated from nuclear holocaust.
By the time a civilization reaches the interplanetary stage to early interstellar flight can usually survive natural disasters, but dangers still remain, from passing stars or the death of their own sun/s. Destruction can befall from technology, such as robotic uprisings and nano-tech disasters. But once a civilization has expanded across the stars it is usually considered immortal. In theory, unfortunatly, this isn't quite true. War with other civilizations, stellar scale disasters can still be a challenge, as well as being stepped on by the Transapient gods. Not all civilizations are extincted. Others evolve on new worlds, either naturally or artificially. Some leave behind artficts or ressurection technologies. Sometimes a dying race may send "gene probes" to spread their descendants around the universe, with child species appearing on new worlds long after the parent race had died out.
By far the worst threat to all life are the Xhodocto, who have scourged this universe and countless others over 14 times in its history. It is believed by some that the Xhodocto are clearing away "old experiments" for new forms.
These are, obviously, extinct. They have been destroyed, or have destroyed themselves.
Ancient times Edit
The Vida'Rra were chronologically the very first living organisms to evolve in this universe. They were no composed of regular matter, being instead composed of a supernatural essense known as Dream Energy. The Vida'Rra scattered around the whole universe, being present in most, if not all existing galaxies. They created a successful and benevolent empire which lasted for about 1.5 billion years, until they ascended to defeat a malevolent being known as Shu'rimrodir. The Vida'Rra seeded much of the universe with life, and their technology is extremely alien to most modern empires. While their empire is know gone, their legacy still exists in their holographic databases, known as Vida'Rranlora.
"Modern era" Edit
Perhraps the two greatest forces of destruction were the Nanohorde and the two most recent scourges.
Believed to be extinct, yet fate or current existence uncertain.
These are civilizations which have since reformed almost completely, or gone in to hiding etc. The species still persists.
The species still persists but have been absorbed into another civuilizaion, either by another of the same species or by another, in any manner neccesary (war, alliances, mind control etc.).