Lengvenis[a] (c. 1360 – after 19 June 1431[1]) was one of the sons of Algirdas, Grand Duke of Lithuania, who was the prince of Novgorod (1389–1392; 1406–1411).

[1] Invited by the Novgorodians themselves, Lengvenis was first regent in Great Novgorod in 1389–1392, responsible to Jogaila, the Grand Duke of Lithuania.

[1] He was baptized in the Eastern Orthodox rite as Semën and received the title of Prince of Great Novgorod.

[1][2] After Lengvenis lost this title in 1392, Vytautas the Great appointed him in 1393 as the Prince of Mstislavl in then eastern Lithuania.

Many historians[clarification needed] believe that under the command of Lengvenis there were three banners of Smolensk land, which played a significant role in the battle.