Nikolaus, Hereditary Grand Duke of Oldenburg was the eldest son of Frederick Augustus II, Grand Duke of Oldenburg, who was the last ruling Grand Duke of Oldenburg.

Frederick Augustus II was the last ruling Grand Duke of Oldenburg. He married Princess Elisabeth Anna of Prussia, daughter of Princess Maria Anna of Anhalt-Dessau and Prince Frederick Charles of Prussia. After her death, he married Elisabeth Alexandrine of Mecklenburg-Schwerin.