Olof Björnsson was a semi-legendary Swedish king, who according to Hervarar saga

Hervarar saga

Hervarar saga ok Heiðreks is a legendary saga from the 13th century combining matter from several older sagas. It is a valuable saga for several different reasons beside its literary qualities. It contains traditions of wars between Goths and Huns, from the 4th century, and the last part is used as...

and the Styrbjarnar þáttr Svíakappa

Styrbjarnar þáttr Svíakappa

Styrbjarnar þáttr Svíakappa is a short story, a þáttr on the Swedish claimant and Jomsviking Styrbjörn the Strong preserved in the Flatey Book ....

ruled together with his brother Eric the Victorious

Eric VI of Sweden

Eric the Victorious was the first Swedish king about whom anything definite is known...

. He was the father of Styrbjörn Starke

Styrbjörn the Strong

Styrbjörn the Strong was, according to late Norse sagas, the son of the Swedish king Olof, and the nephew of Olof's co-ruler and successor Eric the Victorious, who defeated and killed Styrbjörn at the Battle of Fyrisvellir...

 and Gyrid by his queen, Ingeborg Thrandsdotter, and he died of poison

Poison

In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....

 during a meal. Instead of proclaiming his son Styrbjörn co-ruler, Eric proclaimed his own unborn child co-ruler on condition that it was a son. It was a son who became Olof of Sweden.

See also Early Swedish History

Early Swedish history

Swedish pre-history ends around 800 CE, when the Viking Age begins and written sources are available. The Viking Age lasted until the mid-11th century, when the Christianization of Scandinavia was largely completed. The period 1050 to 1350 — when the Black Death struck Europe — is considered the...

.