Danish male given name, derived from the mediaeval Russian name Volodimer, from which, in turn, the modern Russian name Vladimir derives.
There have been four Kings of Denmark by this name:
Valdemar I (1146/1157-1182), called "den Store" ("the Great"), introduced the name into Danish usage, being named after his maternal grandfather Volodimer.
Valdemar II (1202-1241), called "Sejr" ("the Victorious")
Valdemar III (1326-1230)
Valdemar IV (1340-1375), called "Atterdag" ("Day Again")
When an historian refers to Denmark in the "time of the Valdemars", he usually means 1157-1241, the period of the first two kings of this name. This was the historical period of greatest Danish power during the middle ages.
A quasi-legendary version of "King Valdemar" also exists in Danish folklore, who leads a Wild Hunt across the night, frightening God-fearing people out of their wits.
Alternate forms of the name are Waldemar, Volmer. The diminutive, rarely used, is Valde.