Question: Who is Landgravine Marie Louise Of Hesse-Kassel's maternal grandfather?
Answer: Jacob Kettler

Maria Anna Amalia of Courland (12 June 1653 – 16 June 1711) was a Landgravine of Hesse-Kassel through her marriage on 21 May 1673 to her first cousin Charles I, Landgrave of Hesse-Kassel. She was the child of Jacob Kettler and Margravine Louise Charlotte of Brandenburg, eldest daughter of George William, Elector of Brandenburg.