ENDuring his short stay in Lithuania (1434–1445), a modest clergyman from Poland managed to get into the close circle of the Grand Duke and become his informal adviser. It is an example of the unusual career of a man from nowhere, remaining in the shadow of ecclesiastical and secular dignitaries and yet playing a vital role in important political events. He came from a moderately well- -off family at Szadek in the Sieradz district of the Kingdom of Poland. He began his studies at the Faculty of Liberal Arts at the University of Krakow in the winter semester of 1411, finished aft er two semesters in 1412 without being promoted, but still became famous for his rhetorical skills in the future. In the summer of 1434, already as a canon of Vilnius, he represented Grand Duke Sigismund Kęstutaitis at the coronation of Władysław III in Krakow, and a few months later, he was an envoy to the Council of Basel. As a reward for serving Sigismund Kęstutaitis, he was bestowed upon the Vilnius archdeaconry, which the monarch established in 1435. Aft er Grand Duke Casimir Jagiellon ascended the ducal throne, Martinus became an infl uential adviser to the new ruler and, in 1445, supported the latter’s assumption of the Polish throne. He was one of those public figures in the Grand Duchy of Lithuania of the mid-fifteenth century who consistently supported the union and, through personal contacts, united the intellectual cathedral circles of Vilnius and Krakow. Arch deacon Martinus’s last source-verified activity was to be sent to negotiate with the Polish lords gathered at Piotrków (August 1445) and to the border meeting with the Livonian branch of the Teutonic Order (September 1445). Keywords: Martinus de Schadek, archdeacon, diplomat, Grand Duke of Lithuania, University of Krakow.