Alvilda was a Scandinavian pirate in the 5th century. She was the daughter of a king, but left her life as a princess when her father asked her to marry someone she didn't want to marry. Her father wanted her to marry Alf, the crown prince of Denmark. Alvilda did not want to marry Alf and ran away. She and some of her female friends dressed like men and stole a ship. They took the ship into the Baltic Sea as a way of escape. While sailing, they came across a pirate ship without a captain. Alvilda impressed the pirates and they voted her captain.

Alvilda and the pirates were very successful stealing from ships that sailed in the Baltic Sea. Alvilda's pirates attacked many Danish ships, so the King of Denmark sent Alf and his finest men to battle the pirates. Alf attacked Alvilda's ship many times without success. Eventually, in an attack in the Gulf of Finland, Alf was able to board her ship. His men killed most of the her pirates and Alf captured Alvilda. Of course he did not know who she was since she covered her face. When he removed the cover, he was suprised to see Alvilda. Alvilda was so impressed with Alf's courage that she agreed to marry him and to return to Denmark.