Bishop Kos was born into a Croatian Roman Catholic family of Josip and Marija (née Fadiga) in the present-day Varaždin County, but in childhood transferred with own parents and grew-up in Harkanovci.
After graduation of the school education in Široki Brijeg, Bosnia and Herzegovina, he consequently joined the Major Theological Seminary in Đakovo,[1] and was ordained as priest on July 9, 1944 for the Diocese of Bosna, Đakovo and Srijem,[2] after completed his philosophical and theological studies.
[1] On February 6, 1974, he was appointed by Pope Paul VI as the Diocesan Bishop of the Diocese of Đakovo or Bosna and Srijem.
On March 17, 1974, he was consecrated as bishop by Archbishop Mario Cagna and other prelates of the Roman Catholic Church in the Cathedral of St. Peter and St. Paul in Đakovo.
[2] Retired on February 6, 1997, after reached age limit of 75 years old, and was successed by his Coadjutor Bishop.