When looking at Vampires on the Pathfinder wiki, it says that Zura, the Demon Lord of Cannibalism and Vampires, was the first Vampire to have ever existed, which seems natural enough. Also on the page, it makes mention of Ruithvein, the Blood Emperor, who is an Infernal Duke on the sixth layer of Hell.
The page says "The third Vampire to come into being, he descended into the ranks of Hell's nobility" however it makes no mention of who the second Vampire was. I considered the idea of it being Lorcan, as the two compete for the souls of Vampires who have gone to the Nine Hells, however I find it unlikely Lorcan is a Vampire at all, due to there being no mention of it, let alone him being the second Vampire to have ever existed. His areas of concern being blood, undeath, and rebirth however do fit well with the themes of Vampirism, but due to the wiki making no mention of him being a Vampire, I don't think Lorcan is the second Vampire.
We have Zura, the first Vampire ever, who became a Vampire by pulling an Elizabeth Bathory; drinking and bathing in the blood of her subjects to retain her youth and beauty, who became a Demon Lord, and we have Ruithvein, the third Vampire ever, who became a powerful Infernal Duke. It seems to me that Ruithvein became a Vampire after being turned by the second ever Vampire, and if the first Vampire is a Demon Lord, and the second Vampire is an Infernal Duke, I find it hard to imagine the second Vampire ever, who would have been made into a Vampire by Zura herself most likely, is just some no name who didn't accomplish much, save for turning Ruithvein into a Vampire.
If Zura was the first Vampire, and Ruithvein was the third Vampire, who was the second Vampire? Do we know, or at least have some clues to suggest their identity?