Sven Advensen was a retired Imperial Soldier and Count of Darkmoor estate. He had a wife, Lady Inga, and a son, Jonni. He was a distant relative to previous Darkmoor Keep inhabitants and had little to none royal blood.
Sven and his wife were the final caretakers of Barenziah. They raised her as their own daughter, tutored her and allowed her to train her archery skills. However, when Barenziah found out about their "impure" blood, she found them unworthy rulers and considered them mere insects. Barenziah escaped from Sven's estate in age of 16.
He is mentioned in the The Real Barenziah, Book I.