Ivan Vyshens′kyi (c. 1550 to sometime after 1620)—or “Ioann [John] of Vyshnia from the Holy Mountain of Athos”, as he referred to himself in some of his writings—was a Ruthenian Orthodox monk who passed most of his life on Mount Athos and is noted primarily for his writings against the Union of Brest (1595–1596). All of them appear to have been sent in the form of epistles from Mount Athos to the Ruthenian lands; and they were variously addressed not only to the Ruthenian bishops who secured the union, as well as to certain significant religious figures and cultural centers, but also to “all pious people living in Little Rus´ in the Polish Kingdom” (Eremin 1955, 7).
Goldblatt, Harvey, John Mikitish. "Ivan Vyshenskyi". The Literary Encyclopedia. First published 01 August 2019
[https://www.litencyc.com/php/speople.php?rec=true&UID=13648, accessed 24 August 2019.]