Gustav, Landgrave of Hesse-Homburg
Gustav, Landgrave of Hesse- Homburg( 17 February 1781 – 8 September 1848) was landgrave of the German state of Hesse- Homburg from 1846 to 1848.
Margravine Hedwig Sophie of Brandenburg
Hedwig Sophia of Brandenburg( 14 July 1623, Berlin- 26 June 1683, Schmalkalden) was Landgravine consort of Hesse- Kassel by marriage to William VI, Landgrave of Hesse- Kassel, and regent from 1663 until 1677 during the minority of her sons, William VII, Landgrave of Hesse- Kassel and Charles I, Landgrave of Hesse- Kassel.
Charles I, Landgrave of Hesse-Philippsthal
Charles I, Landgrave of Hesse- Philippsthal( 23 September 1682 – 8 May 1770) was a member of the House of Hesse and Landgrave of Hesse- Philippsthal from 1721 until his death.
Chlodwig, Landgrave of Hesse-Philippsthal-Barchfeld
Chlodwig, Landgrave of Hesse ("Chlodwig Alexis Ernst"; 30 July 1876 – 17 November 1954) was an officer in the Prussian Army and head of the Hesse-Philippsthal line of the House of Hesse.
As head of the house he was styled "His Highness the Landgrave of Hesse".
Philip, Landgrave of Hesse-Philippsthal
Philip of Hesse- Philippsthal( 14 December 1655 – 18 June 1721) was the son of William VI, Landgrave of Hesse- Kassel and Hedwig Sophia of Brandenburg.
He was the first landgrave of Hesse- Philippsthal from 1663 to 1721 and the founder of the fifth branch of the house of Hesse.
George III, Landgrave of Hesse-Itter
Landgrave George III of Hesse-Itter (29 September 1632 in Darmstadt – 19 July 1676 in Hof Lauterbach, now part of Vöhl) was the second son of Landgrave George II of Hesse-Darmstadt and his wife Sophia Eleonore of Saxony (1609–1671).
Since he left no male heir, Hesse-Itter fell back to Hesse-Darmstadt.
Sophia Eleonore of Saxony
Sophia Eleonore of Saxony (23 November 1609 – 2 June 1671) was a duchess of Saxony by birth and the landgravine of Hesse-Darmstadt from 1627 to 1661 through her marriage to Landgrave George II.
She was the eldest surviving child of John George I, Elector of Saxony, and Magdalene Sibylle of Prussia.
Prince Frederick William of Hesse-Kassel
Frederick William George Adolphus, Landgrave of Hesse( 25 November 1820 – 14 October 1884) was the only son of Wilhelm I, Landgrave of Hesse- Kassel- Rumpenheim and Princess Louise Charlotte of Denmark.
Ernest Constantine, Landgrave of Hesse-Philippsthal
Ernest Constantine, Landgrave of Hesse-Philippsthal (8 August 1771 in Philippsthal – 25 December 1849 in Meiningen) was a member of the House of Hesse and Landgrave of Hesse-Philippsthal from 1816 until his death.
Moritz, Landgrave of Hesse
Moritz, Prince and Landgrave of Hesse(" Moritz Friedrich Karl Emanuel Humbert" 6 August 1926 – 23 May 2013) was the son of Prince Philip, Landgrave of Hesse, and the head of the House of Brabant and the German House of Hesse.

Question: Who is the maternal grandfather of George Iii, Landgrave Of Hesse-Itter?
Answer: John George I, Elector of Saxony