Martynas Jankus or Martin Jankus (August 7, 1858 in Bittehnen (lit. Bitėnai), near Ragnit – May 23, 1946 in Flensburg, Germany, reburied in Bitėnai cemetery on May 30, 1993) was a Prussian-Lithuanian printer, social activist and publisher in East Prussia, called the Patriarch of Lithuania Minor. He was one of the publishers of Aušra, the first Lithuanian-language newspaper for both Lithuania Minor and Lithuania Major. Jankus used various pen names, including V. Giedris, Martyneitis, Bitėnų Merčius, Gyvoleitis.
After graduating from a primary school in Bitėnai, Jankus continued self-education. From the last decade of the 19th century he was an important figure in the pro-Lithuanian movement, and was close to the Lithuanian National Revival movement in Lithuania. He was one of the founders of several cultural organizations, including Birutė Society, founded in 1885 in Tilsit. From 1889-1892 Jankus was its chairman. In 1890, together with Dovas Zaunius and Jonas Smalakis, Jankus founded the first Lithuanian political organization in East Prussia. He maintained active correspondence with Lithuanian Americans and activists of the Latvian, Polish and Belarusian national movements.
For his public activities Martynas Jankus was penalized by the Prussian authorities about forty times – arrests, monetary fines, and the like. He spent his earnings on the publication of Lithuanian books and newspapers during the Lithuanian press ban in Russia. Jankus was one of the suppliers for the knygnešiai, smugglers of illegal books into Russia. After the Russian Empire occupied the Klaipėda Region in December 1914, Jankus and his family were deported to Samara Governorate in Siberia, where his father and his youngest son Andrius died. In 1918, Jankus returned to his homeland, where he actively promoted the idea of incorporating Lithuania Minor into Lithuania proper. In November 1918 Jankus signed the Act of Tilsit. In 1920 he was co-opted into the Council of Lithuania and later became chairman of the Supreme Salvation Committee of Lithuania Minor. In 1925 Jankus returned to live in Bitėnai.