"I don't know, they came before us, and we spent eons studying them and yet, we still do not know anything about them" -a Zelius Scientist
The Precursors once ruled the entire Multiverse, until their collapse eons before the birth of the Edanian species. They are the earliest known species in the Multiverse. Some astronomists believe they may have created the Multiverse. Not very much to this day is known about them.
Origins
Eons before the creation of the Edanians and many of the other elders, the Precursors ruled the entire Multiverse. Their species goal was to help keep and preserve life, and make sure it never died. They had only one enemy, the Ylikith. The Ylikith were a race of advanced dark organic life forms that wanted to destroy life. The Precursors and the Ylikith had many wars, destroying huge sections of the Multiverse. The Ylikith were destroyed in the Binary War.
Possible Extinction
As their true cause of extinction remains unknown, there is a theory that states the Precursors died of a Multi-Species Plague of which the most accepted theory for this plague origions could come from the extermultiverial Wioni wising to make way for their own invasion of the Multiverse. It effected all of species in the Multiverse at that time. The Precursors were the only species that lasted the longest with the disease. The disease lowerd the immune system's defenses and it hightened both blood pressure and death from psychological problems, such as schizophrenia. The Precursors immune systems were so low that even the common cold could nearly kill them.
Possible Rebirth
though it's only a theory, many believe the ancient and bizarre virus known as the Elder's Virus. The belief that many people hold is that the virus is what happened to the Precursors, that they Evolved (or Devolved depending on who you ask) into a virus in order to survive