The very first Vampire.

“The proper translation is ‘Ashes of the Eldest, Sire of Us All…He was the first of our kind. Burned alive by a jealous Human.“ - Yuvan Rokta, Outbreak in Undercity (RPA-ADV3)

His ashes in the Ancient Sepulchre of Undercity were to be recovered by Yuvan Rokta, who sends you out instead.

A funerary urn in the Undercity Ancient Sepulchre is meant to be The Eldest's final rest place;

The urn upon which he is transfixed is marked with runes that you cannot decipher.

You examine the urn more carefully with your lantern and see that its seal has been broken and its lid removed. The ashes from inside the urn have been scooped out and taken. - Outbreak in Undercity (RPA-ADV3)

However, the ashes are gone, taken by the Starlit Door;

“The people who stole our treasures call themselves the Starlit Door,” the Vampire says to you with his mind. “Find them. Kill them. Bring me what is mine.” - Yuvan Rokta, Outbreak in Undercity (RPA-ADV3)

You recover them from the Library, either by force or in good faith.