Birger Jarl
The marriage between Sophia of Denmark and King Valdemar of Sweden was arranged as a part of the policy of peaceful diplomacy between Denmark and Sweden which was favored by Birger Jarl, Valdemar's father and the de facto Regent of Sweden. In 1254, Birger Jarl had acted as a mediator between Christopher I and King Haakon of Norway, and when Christopher I needed support against Archbishop Jakob Erlandsen of Lund, an alliance was made between Christopher I, King Haakon of Norway and Birger Jarl in 1258. In connection to this, Christopher I engaged his niece Sophia to Birger's son Valdemar of Sweden, and his niece Ingeborg to Haakon's son Magnus VI of Norway.