Сигизмунд Кейстутович
When fighting erupted between Švitrigaila and Sigismund Kęstutaitis for Grand Duke title, Jonas Goštautas supported Sigismund Kęstutaitis, who appointed him as governor of Smolensk later on. He served as governor of Smolensk for around four years until 1440 assassination of Grand Duke Sigismund Kęstutaitis forced him to leave this position. Serving many Duchy rulers he managed to gain and hold tremendous wealth and thus he became one of the richest noblemen of Lithuania.