Nikolaus, Hereditary Grand Duke of Oldenburg (German: Nikolaus Friedrich Wilhelm von Holstein-Gottorp, Erbgroßherzog von Oldenburg; 10 August 1897 – 3 April 1970) was the eldest son of Frederick Augustus II, Grand Duke of Oldenburg, who was the last ruling Grand Duke of Oldenburg.
In 1931, Nikolaus succeeded to his father's titles and assumed the role of pretender to the Grand Duchy, until his death in 1970.
Duchess Ingeborg Alix 20 July 1901 10 January 1996 married Prince Stephan Alexander of Schaumburg-Lippe, a younger son of Georg, Prince of Schaumburg-Lippe.
Duchess Altburg Marie Mathilde Olga 19 May 1903 16 June 2001 married Josias, Hereditary Prince of Waldeck and Pyrmont.