The name Valdemar is a boy's name of Scandinavian, Swedish origin. Valdemar and is often added to lists like Prince Names and discussed in our forums with posts like "Names on NB that make you go WOW!".
From the experts:
Ten years ago we would have advised people to steer clear of this name (and maybe choose the similar sounding Walter instead); but with the rise of other Nordic and Eastern European names like Viggo and Casimir, maybe its time to re-thing Valdemar. It's a big name, but with enough penache, it could be pulled off. Valdemar was introduced to Scandinavia in the 12th Century by a Danish king named for his Ukrainian grandfather, and is currently in the Danish Top 20.