Question: Vaidotas was a son of what ruler of medieval Lithuania who was the Duke of Trakai?
Related documents: [0]  [DOC] Kęstutis (] ; born ca. 1297, died on 3 August or 15 August 1382 in Kreva) was a ruler of medieval Lithuania. He was the Duke of Trakai and governed the Grand Duchy of Lithuania, 1342–82, together with his brother Algirdas (until 1377), and with his nephew Jogaila (until 1381). He ruled over the Lithuanians and Ruthenians. [END] 
[1]  [DOC] Vaidotas or Wojdat (fl. 1362) was a son of Kęstutis, Grand Duke of Lithuania. In reliable historical sources he is mentioned only twice: as defender of Kaunas Castle in 1362 and as ruler of Navahrudak. Due to very limited information, his life is subject to wide-ranging theories by historians. [END] 
Answer: 
Kęstutis
Kęstutis