Jerzy Iwanow-Szajnowicz (Greek: Γεώργιος Ιβάνωφ-Σαϊνόβιτς, Georgios Ivanof-Sainovits; Warsaw, 14 December 1911 – Athens, 4 January 1943) was a Greek-Polish athlete who fought as a saboteur in the Greek Resistance during World War II and was executed by the Germans.
Jerzy Iwanow-Szajnowicz was born in Warsaw on 14 December 1911, as the son of the Russian army colonel Count Vladimir Ivanov, and a Polish mother. His parents divorced soon after. His mother married a Greek, Ioannis Lambrinidis, and together they emigrated to Thessaloniki in northern Greece in 1926.
He became an athlete in the G.S. Iraklis Thessaloniki sport club, and a distinguished swimmer: in 1934, he became Greek champion in 100 m freestyle. After becoming a Polish citizen in 1935, he became part of AZS Warsaw's water polo team and of the Polish national water polo team, and was declared Poland's top water polo player in 1938. Iwanow also graduated from the University of Louvain in agricultural engineering, followed by post-graduate courses at the École nationale supérieure d'agriculture coloniale in Paris, before returning to Greece.
With the outbreak of World War II and the German invasion of Poland, he helped to organize the evacuation of Polish refugees coming to Thessaloniki, and in 1940 was enlisted into Polish intelligence. Fleeing the German invasion of Greece in April 1941, he left the country for the Middle East, to join the exiled Polish forces there. There he was chosen by the Polish and British intelligence services for an undercover mission in Greece. On 13 October 1941, the British submarine HMS Thunderbolt (N25) brought him to the coast of Attica near Nea Makri. His subsequent activity in the Greek underground was prodigious: apart from establishing an extensive intelligence network for the Allies reporting on the military and political situation in Greece, on the Greek war industry, now used by the Germans, and on ship and railway schedules, he engaged in numerous sabotage missions. He was responsible for the sabotage of the German aircraft motor repair facilities in the Maltsiniotis plant, which is credited with affecting over 400 engines and causing the crash of several German aircraft due to engine malfunctions, as well as the destruction of two German U-boats, U-133 and U-372, sabotaging the latter and forcing it to surface and be sunk by the RAF off Haifa.