Mar Youhannan Semaan Issayi (1914 -یوحنا سمعان عیسائی) ;1999)) was the Metropolitan Archbishop of Tehran of the Chaldean Catholics from March 16, 1971, until his death on February 7, 1999.
His excellency Metropolitan Mar Youhannan Semaan Issayi for more than half-century dedicated his life and earnestly served the Assyro-Chaldean Catholic Congregation at Tehran, Hamadan, Kermanshah, Qazvin, and Sanandaj.
A writer of extensively religious or Historic issues in modern Assyrian including an unpublished comprehensive Syriac Dictionary.
Mar Youhannan was editor of the church's periodicals named Marga and Payam published in Persian and modern Assyro-Chaldean.
Mar Youhannan published a poetry book devoted to the Virgin Mary and besides of his clergy services, he was a professor of Aramaic and Assyrian language.