Lengvenis (Simeon Lingwen, born ca. 1360 – died after 1431; Belarusian: Лугвен-Сымон, Łuhvien; Russian: Лугвений, Лугвен, Лугвень, Lugven(y), Polish: Lingwen Semen Olgierdowicz) was one of the sons of Algirdas, Grand Duke of Lithuania, and the ruler of Great Novgorod Republic (1389–1392, 1406–1411). He was known for his skills as a military leader.
Lengvenis was born to Algirdas and his second wife Uliana Alexandrovna of Tver. In 1387 battle with the Teutonic Knights Lengvenis commanded one of Lithuanian formations. In 1389–1392 he was appointed by his brother Jogaila, Grand Duke of Lithuania and King of Poland, as regent of Great Novgorod. He was baptized in the Orthodox rite as Simon and received the title of Prince of Great Novgorod. After Lengvenis lost this title in 1392, Vytautas the Great appointed him to Mstislavl. In 1406–1411 Lengvenis, once again, was nominated by Vytautas as regent of Great Novgorod. As ruler of Novgorod he led battles against Pskov, Livonian Order, and Sweden.
In 1410, Lengvenis participated in the Battle of Grunwald and commanded three banners from Smolensk. His son Yury commanded one of these banners. In 1411 Lengvenis participated in the signing of the Peace of Thorn. He was married to Maria Dmitrovna, princess of Moscow, the daughter of Dmitri Donskoi.
- House of Algirdas – family tree of Lengvenis
- (Lithuanian) Batūra, Romas (2005). "Lengvenis", Vytautas Spečiūnas (compiler) Gediminaičiai. Vilnius: Mokslo ir enciklopedijų leidybos institutas, 184. ISBN 5-420-01558-7
- (Lithuanian) Jučas, Mečislovas (1990). Žalgirio mūšis (Battle of Grunwald). Vilnius: Mokslas, 174. ISBN 5-420-00242-6.