Jonas Kęsgaila was a Lithuanian nobleman, son of Mykolas Kęsgaila

Mykolas Kesgaila

Mykolas Kęsgaila ValimantaitisMykolas is Christian given name, Kęsgaila is pagan given name, and Valimantaitis is patronymic used as last name. His sons used Kęsgaila as their last name. was a Lithuanian nobleman from Deltuva. He established the Kęsgailos family in Samogitia, where their power...

 of the Kęsgaila family. He fathered two sons (Stanislovas Kęsgaila

Stanislovas Kesgaila

Stanislovas Kęsgaila Jonaitis was a Lithuanian nobleman, son of Jonas Kęsgaila from the Kęsgailos family.Stanislovas Kęsgaila was the Elder of Samogitia , Grand Hetman of Lithuania , castellan of Trakai and Vilnius . His main patrimonial property was in Kražiai. Stanislovas was married three...

 and Mykolas Kęsgaila) and two daughters.

Jonas Kęsgaila was Elder of Samogitia

Eldership of Samogitia

The Duchy of Samogitia had been the administrative unit of the Grand Duchy of Lithuania from 1422 . Between 1422 to 1441 it was known as the Eldership of Samogitia...

 (1449–1485), castellan

Castellan

A castellan was the governor or captain of a castle. The word stems from the Latin Castellanus, derived from castellum "castle". Also known as a constable.-Duties:...

 of Trakai

Trakai

Trakai is a historic city and lake resort in Lithuania. It lies 28 km west of Vilnius, the capital of Lithuania. Because of its proximity to Vilnius, Trakai is a popular tourist destination. Trakai is the administrative centre of Trakai district municipality. The town covers 11.52 km2 of...

 (1477) and Vilnius

Vilnius

Vilnius is the capital of Lithuania, and its largest city, with a population of 560,190 as of 2010. It is the seat of the Vilnius city municipality and of the Vilnius district municipality. It is also the capital of Vilnius County...

 (1478–1485). Jonas was a powerful magnate in Samogitia and even conducted independent foreign policy with the Teutonic Knights

Teutonic Knights

The Order of Brothers of the German House of Saint Mary in Jerusalem , commonly the Teutonic Order , is a German medieval military order, in modern times a purely religious Catholic order...

. During the Thirteen Years' War (1454–66), the Samogitians attacked the Knights, including their stronghold in Klaipėda

Klaipeda

Klaipėda is a city in Lithuania situated at the mouth of the Nemunas River where it flows into the Baltic Sea. It is the third largest city in Lithuania and the capital of Klaipėda County....

 (Memel) in 1455. The Samogitian border was closed, disrupting communication between the Teutonic Knights in Prussia

Prussia

Prussia was a German kingdom and historic state originating out of the Duchy of Prussia and the Margraviate of Brandenburg. For centuries, the House of Hohenzollern ruled Prussia, successfully expanding its size by way of an unusually well-organized and effective army. Prussia shaped the history...

 and its branch

Livonian Order

The Livonian Order was an autonomous Livonian branch of the Teutonic Order and a member of the Livonian Confederation from 1435–1561. After being defeated by Samogitians in the 1236 Battle of Schaulen , the remnants of the Livonian Brothers of the Sword were incorporated into the Teutonic Knights...

 in Livonia

Livonia

Livonia is a historic region along the eastern shores of the Baltic Sea. It was once the land of the Finnic Livonians inhabiting the principal ancient Livonian County Metsepole with its center at Turaida...

. These actions are usually interpreted as direct support to Casimir IV Jagiellon

Casimir IV Jagiellon

Casimir IV KG of the House of Jagiellon was Grand Duke of Lithuania from 1440, and King of Poland from 1447, until his death.Casimir was the second son of King Władysław II Jagiełło , and the younger brother of Władysław III of Varna....

, King of Poland. However, this might be oversimplification as the attacks were possibly carried out by unruly Samogitians looking for loot, closing of the border was not considered an ac of war, and Lithuanian nobles generally did not support the war.