While not a canonised Roman Catholic saint, St. Peter of Montenegro's devotion among the Montenegrin Orthodox merits his inclusion here.
King Petar I Petrovic (r. 1782-1830) was made bishop in 1784 and in 1798 he introduced the first law code of Montenegro, killing those tribal leaders opposing the law, and established modern state institutions such as the court system, taxes, schools, police forces, and commercial enterprises. More about him can be learned on Montenet's Petar I Petrovic page.
Peter I was canonised one of the four saints of the Montenegrin Orthodox Church by his successor Petar II Petrovic Njegos (r. 1830-1851). More about the Montenegrin Orthodox Church can be learned on the Montenet Legal Foundations of the Montenegrin Orthodox Church (MOC) page. (All pictures of St. Peter are taken from Montenet.)
In Cettinje, the former capital of Yugoslavia's Montenegro, the Bishop-King Peter is, or at least was, honoured in the annual celebration of Petrov-dan. During this ceremony, it is reported that, at least in former times, the tomb of the Saint was opened so that the ill could venerate the Saint's reportedly incorrupt body, hoping for his intercession for their health. Unfortunately in religious and ethnic wars such as those going on in Yugoslavia relics and other religious objects are often the first victims of ideological struggle, and as yet I am unaware of the current state of the relics of St. Peter and the ceremony of Petrov-dan: Whether the relics are still in existence, whether the festival of Petrov-dan is still celebrated in the ways it once was, or even the date of these ceremonies. In the late 1920's the ceremonies of Petrov-dan were observed by British travellers, a Roman Catholic and a Protestant, and the Catholic's report on the occurrence can be read as following:
Alexander, N. 1927, February. "A Montenegrin Lourdes." The Month, vol. CXLIX, no. 752, pgs. 160-162.