Which Russian ruler and naval commander also took part in polar expeditions to study the Arctic Circle?
Russian polar expedition of 1900–02:  One of the key members of the expedition was Alexander Kolchak, then a young researcher and lieutenant of the Russian Navy, and later a ruler of Russia. Alexander Kolchak: Alexander Vasilyevich Kolchak CB (Russian: Алекса́ндр Васи́льевич Колча́к , 16 November [O.S. 4 November] 1874 – 7 February 1920) was a polar explorer and commander in the Imperial Russian Navy, who fought in the Russo-Japanese War and the First World War.
Alexander Kolchak