Kęstutis (born ca.

1297, died on August 3 or August 15, 1382 in Kreva) is monarch of medieval Lithuania.

He wis the Duke of Trakai and governs the Grand Duchy of Lithuania, 1342–82, together with his brother Algirdas (until 1377), and with his nephew Jogaila (until 1381).

He rules over the Lithuanians and Ruthenians.

The name "Kęstutis" is a derivative from the old form of the name Kęstas, which is a shortened version of such Lithuanian names as Kęstaras, Kęstautas (there kęs-ti means to cope).

Historic writing sources reflect different Lithuanian pronunciation.