Original: When the last duke of Saxe-Wittenberg died without heir in 1422, the Emperor Sigismund gave the duchy to Frederick IV of the house of Wettin, Margrave of Meissen and Landgrave of Thuringia, who thereby became Frederick I, Elector of Saxony.
Simplified: When duke of Saxe-Wittenberg died without an heir in 1422, the Emperor Sigismund gave the duchy to Frederick IV of the House of Wettin. Frederick was already Margrave of Meißen and Landgrave of Thuringia, and then became Frederick I, Elector of Saxony.