Jon Jarl was a legendary Swedish jarl at the end of the 12th and in the early 13th centuries. He is mentioned in Eric's Chronicle from the 1320s to have spent years fighting against Russians and Ingrians in the early Swedish-Novgorodian Wars. No historical evidence on the jarl exists, even though he may be the same "Johannes Dux" who lies buried in the Linköping Cathedral.
According to a 15th century historian Ericus Olai, he was murdered at his home in Asknäs in Ekerö parish by the Lake Mälaren in 1206, allegedly by Russian pirates.