Gertrude of Süpplingenburg (18 April 1115 – 18 April 1143) was Duchess of Bavaria, Margravine of Tuscany, and Duchess of Saxony by marriage to Henry X, Duke of Bavaria, and Margravine of Austria and Duchess of Bavaria by marriage to Henry II, Duke of Austria. She was regent of Saxony during the minority of her son Henry the Lion in 1139–1142.
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Life
Gertrude was the only child of Lothair of Supplinburg, Duke of Saxony, and his wife Richenza of Northeim. After the death of the last Salian emperor Henry V, her father, backed by Archbishop Adalbert of Mainz was elected King of the Romans in 1125, and ruled as Holy Roman Emperor from 1133 to 1137.
First marriage
Gertrude was married to Henry the Proud, Duke of Bavaria, a dynastic arrangement meant to strengthen ties to the Welf dynasty. The lavish wedding ceremony was held on 29 May 1127 on the Lech fields near Augsburg. Indeed, Duke Henry became a loyal supporter in Lothair's struggle with the rivalling House of Hohenstaufen. The marriage also marked a significant increase of the Welf power: in 1136 Lothair vested Henry with the Italian March of Tuscany and, after the death of his father-in-law in 1137, Henry also succeeded him as Duke of Saxony. He furthermore inherited extended Saxon allodial lands around Süpplingenburg, Brunswick and Northeim. According to the contemporary chronicler Otto of Freising he ruled over a realm that stretched "from Denmark to Sicily". Henry and Gertrude had one son, Henry the Lion, born in 1129, who later became Duke of Saxony and Bavaria.