Adolph, Count of Oldenburg-Delmenhorst
Adolph, Count of Oldenburg- Delmenhorst( b. before 1463 – 17 February 1500) was a Count of Oldenburg from 1482 until his death.
John VI, Count of Oldenburg
John VI, Count of Oldenburg( 1501 in Oldenburg – 1548 in Bremen) was a Count of Oldenburg.
He was the eldest son of John V, Count of Oldenburg and his wife, Anna of Anhalt- Bernburg.
He was supposed to rule jointly with his younger brothers.
However, his time in office was marked by conflicts between John VI and his co-rulers.
John V, Count of Oldenburg
John V, Count of Oldenburg and Delmenhorst (also counted as John XIV, including also non-ruling namesake siblings; 1460, Oldenburg – 10 February 1526, Oldenburg) was a member of the House of Oldenburg.
He was the ruling Count of Oldenburg from 1500 to 1526.
His parents were Gerhard VI, Count of Oldenburg and Adelheid of Tecklenburg.
Elimar II, Count of Oldenburg
Elimar II (also Egilmar) was Count of Oldenburg from 1108 through 1142.
He was son of Elimar I, Count of Oldenburg and his wife Richenza.
Elimar married before 1102 Eilika of Werl-Rietberg, daughter of Henry, Count of Rietberg.
Christian II, Count of Oldenburg
Christian II, Count of Oldenburg( died 1233) was a German nobleman.
He was the ruling Count of Oldenburg from 1209 until his death.
Anthony I, Count of Oldenburg
Anthony I, Count of Oldenburg and Delmenhorst( 1505 – 22 January 1573, Oldenburg) was a member of the House of Oldenburg and was the Imperial Count of the Counties of Oldenburg and Delmenhorst within the Holy Roman Empire of German Nation.
His parents were John V, Count of Oldenburg( 1460- 1525) and Anna of Anhalt- Zerbst.
Christian V, Count of Oldenburg
Christian V, Count of Oldenburg( sometimes called" Christian VI"; – after 6 April 1399) was the ruling count of Oldenburg from 1368 until 1398.
He was born sometime before 1347 to Count Conrad I of Oldenburg and Ingeborg of Brunswick.
After his father died in 1368, he ruled Oldenburg jointly with his elder brother Conrad II, and after Conrad II's deaths in 1386, with the latter's son, Maurice II.
He married Agnes of Honstein, and the Danish Royal houses of Oldenburg and Schleswig- Holstein- Sonderburg- Glücksburg descend from him via his son and successor Dietrich, Count of Oldenburg.
Through the dynastic marriages of his descendants, he is an ancestor of many European Royal houses.
Christian, Duke of Oldenburg
Christian, Duke of Oldenburg( born 1 February 1955) is the head of the Grand Ducal Family of Oldenburg.
Christian I, Count of Oldenburg
Christian I, known as "the Quarrelsome" (died 1167) was Count of Oldenburg from 1143 to 1167.
He was son of Elimar II, Count of Oldenburg and his wife Eilika von Werl-Rietberg, daughter of Count Heinrich von Rietberg.
He is a direct male-line ancestor of Margaret II, Queen of Denmark and of King Harald V of Norway, and also of Prince Philip, Duke of Edinburgh, and thus of Charles, Prince of Wales, the heir apparent to the British crown.
Conrad I, Count of Oldenburg
Conrad I of Oldenburg (died 1347) was the Count of Oldenburg from 1344 to 1347.
He succeeded his brother, John III of Oldenburg.
He was the son of John II of Oldenburg and Hedwig of Diepholz.
Conrad married Ingeborg, the daughter of Count Gerhard IV of Holstein-Plön.
They had four children:
Conrad I of Oldenburg is also a male-line ancestor of Queen Margrethe II of Denmark, King Harald V of Norway, and of Philip, Duke of Edinburgh, and thus of Charles, Prince of Wales, and Prince William, Duke of Cambridge.

Question: Who is Christian I, Count Of Oldenburg's paternal grandfather?