Frederick William, Duke of Brunswick-Wolfenbüttel
Frederick William, Duke of Brunswick-Wolfenbüttel (9 October 1771 – 16 June 1815) was a German prince and Duke of Brunswick-Lüneburg and Oels.
Nicknamed "The Black Duke", he was a military officer who led the Black Brunswickers against French domination in Germany.
He briefly ruled the state of Brunswick-Wolfenbüttel from 1806 to 1807 and again from 1813 to 1815.
Henry III, Duke of Brunswick-Grubenhagen
Henry III, Duke of Brunswick- Lüneburg(* 1416 Grubenhagen, † 20 December 1464), of the House of Welf, was a Duke of Brunswick- Lüneburg ruling the ducal Principality of Grubenhagen between 1427 and 1464.
Elizabeth of Denmark, Duchess of Brunswick-Wolfenbüttel
Elisabeth of Denmark (25 August 1573 – 19 July 1625) was duchess consort of Brunswick-Lüneburg as married to Duke Henry Julius of Brunswick-Lüneburg.
She was regent of Brunswick-Lüneburg in 1616-1622.
Francis Otto, Duke of Brunswick-Lüneburg
Francis Otto, Duke of Brunswick- Lüneburg( 1530 – 1559) was the Prince of Lüneburg from 1555 to 1559.
He was the son of Ernest I, Duke of Brunswick- Lüneburg.
Matilda of Brunswick-Lüneburg
Matilda of Brunswick- Lüneburg( 1276 – 26 April 1318) was a German noblewoman and member of the House of Welf.
By birth, she was a duchess of Brunswick- Lüneburg and by marriage Duchess of Glogów, Ścinawa, etc.
She was the seventh child and only daughter of Albert I, Duke of Brunswick- Lüneburg by his second wife Alessina, daughter of Margrave Boniface II of Montferrat.
Dorothea of Brunswick-Lüneburg
Dorothea of Brunswick-Lüneburg (1 January 1570 – 15 August 1649) was a daughter of Duke William "the younger" of Brunswick-Lüneburg and his wife, Dorothea of Denmark, Duchess of Brunswick-Lüneburg.
She married Count Palatine Charles I of Zweibrücken-Birkenfeld.
They had four children:
Duke Louis Ernest of Brunswick-Lüneburg
Louis Ernest of Brunswick- Lüneburg- Bevern( 25 September 1718, Wolfenbüttel – 12 May 1788, Eisenach) was a field- marshal in the armies of the Holy Roman Empire and the Dutch Republic, the elected Duke of Courland( 1741).
From 13 November 1750 to 1766 he was the Captain- General of the Netherlands, where he was known as the Duke of Brunswick or( to distinguish him from his eldest brother Charles, who succeeded to their father's title of Duke of Brunswick- Lüneburg) Duke of Brunswick- Wolfenbüttel.
Another brother was Duke Ferdinand of Brunswick who led the Allied Anglo- German army during the Seven Years' War.
He was probably one of the first victims of the media in Dutch history.
Albert I, Duke of Brunswick-Lüneburg
Albert the Tall (1236 – 15 August 1279), a member of the House of Welf, was Duke of Brunswick-Lüneburg from 1252 and the first ruler of the newly created Principality of Brunswick-Wolfenbüttel from 1269 until his death.
William I, Duke of Brunswick-Lüneburg
William (c. 1270 – 30 September 1292 in Brunswick), Duke of Brunswick-Lüneburg, briefly ruled part of the duchy.
William was the third son of Albert I, Duke of Brunswick-Lüneburg.
On Albert's death on 1279, the three eldest brothers succeeded him, but were put under guardianship of Conrad, Prince-Bishop of Verden.
After they reached majority, they divided the territory among each other in 1291:
William received the northern part of their father's state, including Brunswick, Schöningen, the Harzburg, Seesen, and Königslutter.
The brothers disagreed over control of the City of Brunswick.
Only a year later, William died, and his brothers divided his territory among each other.
He had married Elizabeth, daughter of Henry I, Landgrave of Hesse, but the marriage apparently remained childless.
Henry the Peaceful, Duke of Brunswick-Lüneburg
Henry the Peaceful( 1411 – 7 December 1473), Duke of Brunswick- Lüneburg, called the Peaceful, ruled over both parts of Brunswick- Lüneburg.

Question: When did William I, Duke Of Brunswick-Lüneburg's father die?
Answer: 15 August 1279