He was probably the same person as the Sverinius who is mentioned as the first Bishop of Uppsala in an early 15th-century Incerti scriptorts Sueci chronicon primorumin ecclesia Upsalensi archiepiscoporum, chronicle of Uppsala archbishops.
[1] Historical sources mention Siwardus in 1142 and 1143.
Siwardus apparently died in a monastery in Oldenburg in 1159 after being exiled from Uppsala by local heathens sometime earlier.
There were plans to have him canonized as a saint, which never took place.
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