Prince Nicholas of Greece and Denmark
Prince Nicholas of Greece and Denmark (22 January 1872 – 8 February 1938), of the Glücksburg branch of the House of Oldenburg, was the fourth child and third son of King George I of Greece, and of Queen Olga.
He was known as "Greek Nicky" in the family to distinguish him from his paternal first cousin Emperor Nicholas II of Russia.
Prince Nicholas was a talented painter, often signing his works as "Nicolas Leprince."
Grand Duchess Olga Pavlovna of Russia
Grand Duchess Olga Pavlovna of Russia  was a "Grand Duchess of Russia" as the second youngest daughter and seventh child of Emperor Paul I of Russia and his empress consort, Sophie Dorothea of Württemberg.
Ogawa Mataji
Viscount was a general in the early Imperial Japanese Army.
He was also the father- in- law of Field Marshal Gen Sugiyama.
Princess Charlotte of Württemberg
Princess Charlotte of Württemberg (9 January 1807 – 2 February 1873) was later known as Grand Duchess Elena Pavlovna, the wife of Grand Duke Michael Pavlovich of Russia.
He was the youngest son of Emperor Paul I of Russia and Duchess Sophie Dorothea of Württemberg.
Prince Dmitri Alexandrovich of Russia
Prince Dmitri Alexandrovich of Russia( 15 August 1901 – 7 July 1980) was the fourth son and fifth child of Grand Duke Alexander Mikhailovich of Russia and Grand Duchess Xenia Alexandrovna of Russia.
He was a nephew of Tsar Nicholas II of Russia.
Abdul-Vahed Niyazov
' of Russia.
Princess Elizabeth of Greece and Denmark
Princess Elisabeth of Greece and Denmark( 24 May 1904 – 11 January 1955) was the middle daughter of Prince Nicholas of Greece and Grand Duchess Elena Vladimirovna of Russia.
Grand Duchess Maria Vladimirovna of Russia
Grand Duchess Maria Vladimirovna of Russia (born 23 December 1953 in Madrid) has been a claimant to the headship of the Imperial Family of Russia (who reigned as Emperors and Autocrats of All the Russias from 1613 to 1917) since 1992.
Although she has used Grand Duchess of Russia as her title of pretence with the style Imperial Highness throughout her life, her right to do so is disputed.
She is a great-great-granddaughter in the male line of Emperor Alexander II of Russia.
Grand Duchess Elena Pavlovna of Russia
Grand Duchess Elena Pavlovna of Russia, Hereditary Grand Duchess of Mecklenburg( 24 December 1784[ OS 13 December] – 24 September 1803) was a daughter of Grand Duke, later Tsar Paul I of Russia and his second wife Sophie Dorothea of Württemberg.
After marrying the son and heir of the Grand Duke of Mecklenburg- Schwerin she ceased to use her Russian title.
Grand Duchess Elena Vladimirovna of Russia
Grand Duchess Elena Vladimirovna of Russia (17 January 1882 – 13 March 1957), sometimes known as Helen, Helena, Helene, Ellen, Yelena, Hélène, or Eleni, was a Russian grand duchess as the only daughter and youngest child of Grand Duke Vladimir Alexandrovich of Russia and Duchess Marie of Mecklenburg-Schwerin.
Her husband was Prince Nicholas of Greece and Denmark
and they were both first cousins of Emperor Nicholas II of Russia.

Question: Who is the father-in-law of Grand Duchess Elena Vladimirovna Of Russia?
Answer: George I of Greece