"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 (known by their original name of Ai'kijak) 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 astronomers believe they may have created the Multiverse. Not very much to this day is known about them.
Origins
Eons before the birth 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 matter 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. however, no one knows what the Precursors looked like, their homeworld, what was their culture truly like, or how they evolved, but, many have theorized that the Precursors were largely an arachnid like species, this theory have many supporting evidence for it, given the few remaining Precursors statues found within the surviving Precursor Temples often had an arachnid appearance
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 origins 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
The Last Precursors
though no knows how they become immortal, some saying that they used advanced technology to make themselves immortal or rather, never age again, others say they become immortal by asking a Mort to extend their lives. Whatever the case maybe, these two individuals are, by every account, the last of their kind, unfortunately, they are also sterile, as a side effect of the Wionis Plague, thus, any hope to resurrect the species have went away just like the Ancient Precursors, though, the Federation have created a project to try and resurrect the species by using the two DNA to at least create fertile clones to slowly revive the species.