John Sigismund was a Prince-elector of the Margraviate of Brandenburg from the House of Hohenzollern. He became the Duke of Prussia through his marriage to Duchess Anna, the eldest daughter of Duke Albert Frederick of Prussia who died without sons. Their marriage resulted in the potential creation of Brandenburg-Prussia, which became a reality after Poland's leader appointed John Sigismund in charge of Prussia in regency and, shortly thereafter, Albert Frederick died without an able, direct male heir.

The Margraviate of Brandenburg was a major principality of the Holy Roman Empire from 1157 to 1806 that played a pivotal role in the history of Germany and Central Europe.