Dr Jan Petersen (born 1887; full name: Jan Greve Thaulow Petersen) was a Norwegian historian notable for writing De Norske Vikingsverd ("The Norwegian Viking Swords") in 1919. This book was the "standard and authoritative work" on Norse sword typology and "remains an invaluable guide today."[1] The Oakeshott typology is based on Petersen's work.
An online English translation of De Norske Vikingsverd is available here.