Who married Valentina Šimkuvienė?

Kęstutis (c. 1297 – 3 or 15 August 1382) was sole Duke of Trakai from 1342 to 1382 and Grand Duke of Lithuania from 1342 to 1382, together with his brother Algirdas (until 1377), and with his nephew Jogaila (from 1377 to 1381).

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.