The Chronicon Lethrense and the included Annales Lundenses tell that Haldan (Healfdene) had two sons, Helghe (Halga) and Ro (Hrodgar). When Haldan died of old age, Helghe and Ro divided the kingdom so that Ro ruled the land, and Helghe the sea. One day, Helghe arrived in Halland/Lolland and slept with Thore, the daughter of one of Ro's farmers. This resulted in a daughter named Yrse. Much later, he met Yrse, and without knowing that she was his daughter, he made her pregnant with Rolf. Eventually, Helghe found out that Yrse was his own daughter and, out of shame, went east and killed himself.  Both Helghe and Ro being dead, a Swedish king, called Hakon in the Chronicon Lethrense proper, and Athisl in the Annales - corresponding to Eadgils - forced the Danes to accept a dog as king. The dog king was succeeded by Rolf Krage.  Rolf Krage was a big man in body and soul and was so generous that no one asked him for anything twice. His sister Skulda was married against Rolf's will to Hartwar or Hiarwarth (Heoroweard), a German earl of Skane, but reputedly Rolf had given Skulda to him together with Sweden.  This Hartwar arrived in Zealand with a large army and said that he wanted to give his tribute to Rolf, but killed Rolf together with all his men. Only one survived, Wigg, who played along until he was to do homage to Hartwar. Then, he pierced Hartwar with a sword, and so Hartwar was king for only one morning.

Answer this question "What did the Swedish king do?" by extracting the answer from the text above.
forced the Danes to accept a dog as king.