Few things are known about Leopold Valdemar. Apparently, he came from the lineage of Boukephos and originated in Denmark. He apparently enjoyed the trust of both Augustus and Claudius Giovanni, who let him in on parts of the plan for the Endless Night.
A bald, middle-aged man, he was a hearty fellow, who does many things to excess, even things that would give other Kindred "nightmares" for months on end. He seldom, if ever, gave credence to the idea that limits should be applied to his behavior. This might have contributed to his disdain against the Founders and his support for the Conspiracy.
Either during the final confrontation with the Founders and the Children of Isaac or before, Leopold Valdemar met Final Death. His spirit became a wraith fettered to Claudius Giovanni's ruined castle that was attacked in 1444. Ambrogino Giovanni splintered his essence around the place as a punishment, causing him constant agony, as a collective punishment for the Conspiracy's final failure.
In the 5th edition of Chicago by Night it was revealed that Lord Valdemar was actually the sire of the famous Lasombra known as Talley, the Hound. That is unnusual, to say the least, as Talley was embrace around 1355 - a period when Valdemar himself should be long dead.
- Note: His extra level of Obtenebration allows him to use the darkness to suck blood from others and give his own shadow substance (via The Darkness Within)