Professor Masing was born to a peasant family in Estonia. He lectured at Tartu University and was known as a humanist and an anti-fascist. In 1939, he was invited to lecture at the Hebrew University in Jerusalem, but the outbreak of war prevented his visit. During the Nazi occupation, Masing was singled out by the occupying forces as a subversive element. During the occupation, Masing refused to teach at the university, and worked to salvage Jewish cultural and religious artifacts. Isidor Lewin, an Estonian Jew, was Masing’s student and neighbor. He decided to hide from the authorities. Masing knew of Lewin’s Jewish identity, and as of 1943, with his wife Eha assisted Lewin by supplying him with food and other needs on a steady basis. Not only did Uko Masing risk his life by maintaining contact with a Jew, he also provided Lewin with forged documents, gave false testimony to the Gestapo, and provided Lewin with shelter and food.
After the war, Masing was active on a committee which investigated Nazi crimes. He participated in the inquiry into the events in the Klooga Camp to where many Jews were deported and killed.