The sexton of Puhja Church Käsu Hans (Kässo Hantz, Hans Kes, Käßo Hanß) is considered to be the first Estonian poet. His 32-verse lament on the tragic fate of the town of Tartu in the Great Northern War (1709) is the first work of literatuure in the Estonian mother tongue in Estonian cultural history. Villem Reiman published this lament at the end of the 19th century. Reiman also found and published a letter written by Käsu Hans in Estonian from 1706. The letter was addressed to Pastor Könik Könikson. Reiman called it the oldest letter written by an Estonian. Another two letters written by Käsu Hans in 1702 and 1703 addressed to Professor Gabriel Skragge are preserved in Riga at the Latvian National History Museum. These two letters are published for the first time in this article. Another letter from 1706 is published together with them. This letter was for a long time thought to be lost and its original is preserved at the Estonian Literary Museum in Tartu. Very little is known about the course of the life of Käsu Hans. The dates of his birth and death are not known, likewise the dates of his career as sexton. The assumptions of scholars who have hitherto studied his life and work (V. Reiman, Fr. G. Bienemann, A. Annist and others) contradict one another. The new standpoints presented in this article are founded on the letters written by Käsu Hans and on original sources in the archives in Tartu and Riga. The analysis supports the hitherto existing assumptions that Käsu Hans was born in Puhja Parish in the hamlet of Teilma around 1670 and studied in Tartu at the school run by Bengt Gottfried Forselius, where Estonian schoolmasters were trained in 1684–1686. It is quite likely that he already became the schoolmaster at Puhja in 1686 and later became the local sexton as well. Adrian Virginius, the pastor of Puhja Church, can be considered his most important mentor. In a letter sent to Professor Gabriel Skragge, Käsu Hans requests written confirmation of the land allotted to the schoolmaster to cover his salary so that he would not lose the grain that he had sown there himself in the event that he leaves his position. Puhja Church had been Skragge’s prebend in 1694–1700. In his letter to Könik Könikson, the pastor of Puhja Church who had taken refuge from the war in Pärnu, Hans the sexton conveyed news on the war situation and the life of the congregation. The letters written by Käsu Hans are unique documents that bear witness to the level of education of the first Estonians who had received education at school. They are also the earliest sources that enable us to study the language written by a native speaker of Estonian. Käsu Hans died probably around 1709.