Theodor Kristian Avellan (Russian: ????? ???????? ??????, Fyodor Karlovich Avelan; 12 September 1839 – 30 September 1916) was a Finland-Swedish admiral in the Imperial Russian Navy, noted for his role in the Russo-Japanese War of 1904-1905.
Although castigated by the Russian government for the defeat of Russia in that war, he subsequently served on the Board of Admiralty and was member of the State Council (1914).