Erdmonas Simonaitis (30 October 1888 – 24 February 1969) was a Prussian Lithuanian activist particularly active in the Klaipėda Region (Memel Territory) and advocating its union with Lithuania.

[3] According to the Treaty of Versailles, the Klaipėda Region (Memel Territory) was detached from the German Empire and placed under provisional French administration.

French General Dominique Joseph Odry [pl] established seven-member Directorate (local government) in February 1920.

[4] Simonaitis lobbied the League of Nations and the Conference of Ambassadors to unite the Klaipėda region with Lithuania.

Therefore, the Lithuanian government decided to organize the Klaipėda Revolt, take the region by force, and present a fait accompli.

[2] In March 1939, Nazi Germany presented an oral ultimatum to Lithuania demanding to cede the Klaipėda Region.

After the occupation of Lithuania by Nazi Germany in June 1941, Simonaitis was arrested by the Gestapo and sent to the Mauthausen-Gusen concentration camp in November 1942.

They changed their names to Elena and Ona in an attempt to hide their German descent and returned to Klaipėda.