Jancko Douwama was a Frisian nobleman who fought to free Friesland from foreign rule during the Vetkopers and Schieringers conflict, the Saxon feud and the Guelders Wars.
Jancko Douwama lived in much troubled times during the final stages of a civil war in Friesland between the monastical factions called the Vetkopers and Schieringers.
[citation needed] In 1521 Jancko swore an oath of allegiance to the Holy Roman Emperor Charles V of Habsburg, the arch-enemy of the Duke of Guelders.
Whilst imprisoned in the castle of Vilvoorde, Jancko wrote his memoirs, titled the 'Boeck der Partijen' (Book of the Parties) which is considered one of the oldest written autobiographies.
The memoirs gives Jancko's definition of the terms Schieringers and Vetkopers; 'Vetkopers' (fatbuyers) were so called because they had much and could buy fat products.