He is mentioned in Erik's Chronicle from the 1320s to have spent years fighting against Russians and Ingrians in the early Swedish–Novgorodian Wars.
According to 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.
[1] According to Erik's Chronicle, Jon Jarl was a Swedish earl in the east tasked with the protection of the kingdom against Russians and Ingrians.
The Chronicle states: Jon's wife fled across the bay to Hundhamra (i.e. Norsborg), and gathered a mob to kill the perpetrators.
[citation needed] No historical evidence on the jarl exists, although he may be the "Johannes Dux" who is shown on an undated tombstone also labelled "Terror of the heathens" Linköping Cathedral.