Lilith also known as the Progenitor is supposedly the "first vampire", made in God's image. She's believed by many vampires to have been created before Adam and Eve, who, according to the Original Testament, were both designed to be her food and to sustain her and her offspring.
In the fifth episode of season five it is revealed that within the Authority's chamber there is a vile of blood that many believe to have belonged to Lilith. However, Roman explains to Salome that the blood is not Lilith's. And by allowing others to believe that the blood belongs to Lilith he boosts his own, and the Authority's credibility. This would lend to the idea that Lilith, for whatever reason, no longer exists or possibly never existed though she could be real but vampires deem her to be a myth.
Dieter and Rosalyn also seem to know the blood is not Lilith's as they openly mock the vampire bible and deny her existence.
