Louis VI, Landgrave of Hesse-Darmstadt
Louis VI of Hesse-Darmstadt  (25 January 1630 – 24 April 1678) was Landgrave of Hesse-Darmstadt from 1661 to 1678.
He was the eldest of three sons of the Landgrave George II of Hesse-Darmstadt and Sophia Eleonore of Saxony.
Princess Mary of Great Britain
Princess Mary of Great Britain (5 March 1723 – 14 January 1772) was the second-youngest daughter of King George II of Great Britain and his wife, Caroline of Ansbach, and Landgravine of Hesse-Kassel as the wife of Frederick II, Landgrave of Hesse-Kassel.
Louis VIII, Landgrave of Hesse-Darmstadt
Louis VIII (German: "Ludwig") (5 April 1691 – 17 October 1768) was the Landgrave of Hesse-Darmstadt from 1739 to 1768.
He was the son of Ernest Louis, Landgrave of Hesse-Darmstadt and Margravine Dorothea Charlotte of Brandenburg-Ansbach.
Sophia Eleonore of Hesse-Darmstadt
Sophia Eleonore of Hesse- Darmstadt( 7 January 1634 in Darmstadt – 7 October 1663 in Bingenheim, now part of Echzell), was Landgravine of Hesse- Darmstadt by birth and by marriage Landgravine of Hesse- Homburg.
She was a daughter of Landgrave George II of Hesse- Darmstadt( 1605 – 1661) from his marriage to Sophia Eleonore( 1609 – 1671), the daughter of Elector John George I of Saxony.
Louis V, Landgrave of Hesse-Darmstadt
Louis V of Hesse-Darmstadt (24 September 1577 – 27 July 1626) was the Landgrave of Hesse-Darmstadt from 1596 to 1626.
He was born on 24 September 1577 as the son of George I, Landgrave of Hesse-Darmstadt and Magdalene of Lippe.
In 1604 he inherited a part of Hessen-Marburg after the death of Louis IV of Hesse-Marburg who was childless.
The other half went to Maurice of Hesse-Kassel (or Hesse-Cassel), but since Maurice was a Calvinist, Ludwig claimed a right on the whole of Hesse-Marburg.
Lutheran professors of the University of Marburg who refused to convert to Calvinism founded in 1607 the University of Gießen which was named "Ludoviciana".
This led to a conflict during the Thirty Years' War, between Louis V, who stood on the side of the Emperor, and Maurice, who was on the side of the Protestants.
Hesse-Darmstadt suffered severely from the ravages from the Swedes during the conflict.
The Landgrave died in 1626 and he was succeeded by George II, Landgrave of Hesse-Darmstadt.
In 1722, Johann Georg Liebknecht, an astronomer at the University of Gießen, named a star, which he thought was a planet, Sidus Ludoviciana after Ludwig V.
George II, Landgrave of Hesse-Darmstadt
George II of Hesse-Darmstadt, (17 March 1605, in Darmstadt – 11 June 1661) was the Landgrave of Hesse-Darmstadt from 1626 to 1661.
He was the son of Ludwig V and Magdalene of Brandenburg.
He married Sophia Eleonore of Saxony on 1 April 1627.
From 1645 to 1648 he led the so-called "Hessenkrieg" against the Landgravine Amalie Elizabeth of Hesse-Kassel over the inheritance of the extinct line of Hesse-Marburg.
This conflict resulted in the loss of Hesse-Marburg to Hesse-Kassel.
Adelaide of Hesse
Adelaide of Hesse( after 1323 – after May 26, 1371) was a daughter of Henry II, Landgrave of Hesse, and his wife Elisabeth of Thuringia, daughter of Frederick I, margrave of Meissen.
Adelaide was a member of the House of Hesse.
William II, Landgrave of Hesse-Wanfried-Rheinfels
William II, Landgrave of Hesse- Wanfried- Rheinfels( also known as" William the Younger"; born: 25 August 1671 in Langenschwalbach; died: 1 April 1731 in Paris, and also buried there) was a son of the Landgrave Charles of Hesse- Wanfried( 1649 – 1711) and his first wife, Sophie Magdalene of Salm- Reifferscheid( d. 1675).
He succeeded his father as Landgrave of Hesse- Wanfried and Hesse- Rheinfels.
After 1711, he styled himself" Landgrave of Hesse- Rheinfels".
William I, Elector of Hesse
William I, Elector of Hesse( 3 June 1743 – 27 February 1821) was the eldest surviving son of Frederick II, Landgrave of Hesse- Kassel( or Hesse- Cassel) and Princess Mary of Great Britain, the daughter of George II.
Magdalene of Brandenburg
Magdalene of Brandenburg, also Magdalene and Magdalen, (7 January 1582 – 4 May 1616) was the daughter of John George, Elector of Brandenburg and his third wife Elisabeth of Anhalt-Zerbst.
She married Louis V, Landgrave of Hesse-Darmstadt.

Question: Who is George Ii, Landgrave Of Hesse-Darmstadt's maternal grandfather?
Answer: John George, Elector of Brandenburg