Kęstutis

Kęstutis became Duke of Trakai around 1342, a position he maintained for four decades. For most of that time he's believed to have ruled the Grand Duchy of Lithuania jointly with his brother Algirdas, a power-sharing arrangement that lasted until 1377. After Algirdas's death, the balance shifted: Kęstutis governed alongside his nephew Jogaila for another four years. That partnership ended in August 1382, when Kęstutis died—sources give either the 3rd or the 15th as the date.