Valdemar is an Ghost Nord Blade inside Sancre Tor. He was one of the mightiest Blades from the time of Tiber Septim, but now guards the prison section of Sancre Tor. He, along with Rielus, Casnar and Alain, were trapped there.
Martin tells the Hero that he has deciphered the next part of the Mysterium Xarxes. He claims that he needs the sacred blood of one of the divines, manifest in the ancient armor of Sancre Tor in order to fulfill his mission.
"I know you. You freed me. Free my brothers, if they are still enslaved. Together we will cleanse the Shrine of the Underking's foul magic."
(After the curse is lifted)
"We have fulfilled our last duty. We go now to Aetherius without shame. Farewell."
- The Elder Scrolls IV: Oblivion (Appears as a ghost or a spirit)