Kęsgailos was a Lithuanian noble family, one of the biggest landowners in the Grand Duchy of Lithuania. The family traces its roots to the 14th century AD (Buseika is considered the ancestor of the family). Their seat was in the Samogitia and Trakai regions. Kęsgailos family members had been the Elders of Samogitia from 1412 until 1532.
According to the 1528 military inventory documents, the family provided the biggest number of troops in the Grand Duchy of Lithuania [1]. The family died out in the 16th century.
The surname Kęsgaila comes from the first name of Mykolas Kęsgaila son of Valimantas, whose elder brother Jaunutis son of Valimantas was granted the Zadora Coat of Arms in the Union of Horodlo of 1413. In line with the common practice for nobles' names after the Christianization of Lithuania, after his baptism, the Christian name *Mīkālas (Michael) was added to a pagan Lithuanian name, which can be reconstructed as *Kensgaĭla (from kęsti ("be patient") and gailas ("strong")). His son Jonas Kęsgailaitis, mentioned in written sources in Latin as Johannes Kyensgalowicz[2], was a bearer of the name as a patronymic, which subsequently evolved into a family name. Its Polonized form Kieżgajło is most common in Polish historiography over other variants, such as Kezigal, Kieżgajłła, Gezgajło, Kiezgajło, Kieżgajłło, Kierżgajłło, Kieżgałło and Kieżgało. Kęsgaila (plural Kęsgailos) is a modern Lithuanian spelling of the original family name.