Alopaeus (sometimes transliterated as Alopeus) is a Finnish family, originating from Vyborg. Some family members have fennicized the name to Kettunen or Tuomas-Kettunen. Notable family members include: * Johan Alopaeus (1731 - 1811), ennobled in 1772 with the name Nordensvan * Maximilian von Alopeus (1748—1822), Russian diplomat * Frans David Alopaeus (1769—1831), his brother, also a diplomat * Fredrik Alopaeus (1810 - 1862), Finnish general in Imperial Russian Army, son of David * Maunu Jaakko Alopaeus, Bishop of Porvoo 1809-1818 * Carl Henrik Alopaeus, Bishop of Porvoo 1885-1892 * Erik Alopaeus, first Finnish Parliamentary Ombudsman in 1920 * Marianne Alopaeus (b. 1918), Finnish author