Henry I, Duke of Brunswick-Lüneburg, called the Admirable, a member of the House of Welf, was the first ruler of the Principality of Grubenhagen from 1291 until his death.
Background
He was the eldest son of the Brunswick duke Albert the Tall and his second wife Adelaide, daughter of Margrave Boniface II of Montferrat. His father had ruled the Duchy of Brunswick-Lüneburg jointly with his brother John, until both divided their territory in 1269.
Career
Albert went on to rule the Principality of Wolfenbüttel until his death in 1279. In 1291 they again divided the territory. Henry received the part that came to be known as Principality of Grubenhagen.
lieutenant included the cities of Einbeck, half of Hamelin, Clausthal, Amelungsborn, Duderstadt, Herzberg, and Osterode.
He took Einbeck as his residence. In 1320, Henry was appointed Count Palatine of Saxony by the emperor.
He died in 1322, and his three surviving sons who had not joined the Church divided his territory among each other. Henry married Agnes, daughter of Albert the Degenerate, Margrave of Meissen, in 1282.
They had 16 children:
Elizabeth (born c 1282), married Frederick, Count of Beichlingen
Otto (born c 1283, died in or before 1309)
Albert (born c 1284, died after 1341), joined the Teutonic Order
Adelaide (1285–1320), married King Henry I of Bohemia
Facie (daughter.
Born c 1286, died before or in 1312)
Agnes, Abbess of Osterode (born c 1287, died between 1332 and 1336)
Henry (born c 1289, died before or in 1351)
Frederick (c 1291 – c 1323)
Adelheid of Brunswick (c 1293 – 17 August 1324), married Andronikos III Palaiologos, Roman Emperor
Conrad (c 1294 – c 1320)
Mechtild (c 1295 – between 24 October 1333 and 14 March 1344), married John II of Werle
Ernest (c 1297 – 11 March 1361)
William (c 1298–1360)
Richardis, Abbess of Osterode (born c 1300, died between 1332 and 1336)
Margaret (born c 1300, died in or after 1312)
John, (born before 1322, died 23 May 1367), provost at Einbeck.