Lilith is an Ancient.
Lilith was an Ancient scientist who researched the Wraith. She eventually started doing experiments on M1M-316 where millions of years ago, the Ancients had experimented on dinosaurs for the possibility of using telepathy and empathy for Ascension. After the Ancients were forced to flee the Pegasus Galaxy, Lilith continued her work, believing that the Ori needed to be stopped. She began creating chimeras, creatures that would eventually turn into the monsters of mythology. Most were not viable, but she was eventually able to create the Lilin. The Ancients ordered her to stop, but she refused, making her a martyr to her creations. While Lilith's original intent was to battle the Ori, her obsession drove her insane and she became as bad the Ori. Eventually, her laboratory was destroyed by a great flood and the Sumerian King Gilgamesh built her a sanctuary. She eventually vanished, likely to Egypt, but not before indoctrinating in the Lilin that they were descendants of the Wraith and they had a sacred duty to protect "them" from the Ori. The Lilin later split into the Lilith and Ninlil factions with the Lilith believing she meant the Ancients while the Ninlil believe she meant all sentient life. What happened to Lilith afterwards isn't known for sure, but Doctor Daniel Jackson found information on a cave wall and the Gilgamesh tablets that indicates she was killed by the Goa'uld System Lord Nirrti. Daniel theorizes that Nirrti, who was known for her genetic experimentation, was either a student of Lilith or took her as a host to get her knowledge before she was killed. (SGA: "Blood Ties")