Patriarch Alexy II (or Alexius II, Russian: Святе́йший Патриа́рх Моско́вский и всея́ Руси́ Алекси́й II; secular name Alexey Mikhailovich Ridiger Russian: Алексе́й Миха́йлович Ри́дигер; 23 February 1929 – 5 December 2008) was the 15th Patriarch of Moscow and All Russia, the primate of the Russian Orthodox Church.

His name (secular Алексей, clerical Алексий) is transliterated from the Cyrillic alphabet into English in various forms, including Alexius, Aleksij, Aleksi, Aleksiy, Alexiy, Alexis, Alexei, Alexey, and Alexy. When he became a monk, his name was not changed, but his patron saint changed from Alexius of Rome to Alexius, Metropolitan of Moscow whose relics repose in the Epiphany Cathedral in Moscow.

Elected Patriarch of Moscow one and half year prior to the Soviet Union's collapse, he became the first Russian Patriarch of the post-Soviet period.