Swedish jarls

In Sweden, members of medieval royal families, such as the House of Stenkil and House of Bjelbo, held the title of jarl before their accession to the throne. Since the early 12th century, there usually was only one holder of the title at a time, second only to the King of Sweden.

For special occasions, regional jarls outside of Sweden could be nominated as well. An example of this is Jon Jarl, who allegedly conducted pirate operations against Novgorod in the east. When the House of Bjelbo (alt. Bjälbo) succeeded in becoming the royal family in 1250, the title was subsumed into that of duke and the powers were merged into the kingship soon after Birger Jarl's death in 1266.

According to Procopius, the Heruli, after having raided the European continent for several generations, returned to Scandinavia in 512 as a result of military defeats. As their old territory was now occupied by the Danes, they settled next to the Geats in present-day Sweden. While the Proto-Norse word for this mysterious tribe, erilar, is etymologically near the title "jarl" and "earl" in other places, perhaps implying ' those who can read or dictate ' and it has often been suggested they introduced the runes in Scandinavia, no elaborate theory exists to explain how the word came to be used as a title. Arguably, their knowledge in interpreting runes also meant they were gifted in martial arts and, as they gradually integrated, eril or jarl instead came to signify the rank of a leader. As described in the Icelandic sagas, such as Rígsthula, a jarl was a sort of chieftain next in rank to the king in the function of Marshal or Duke of the King's Army. Under any circumstance, when jarls are finally mentioned in medieval documents, it clearly was a title signifying a leader ranked directly under the king.

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