Petar (Bulgarian: Петър, Serbian Cyrillic: Петар) is a South Slavic masculine given name, their variant of the Biblical name Petros cognate to Peter. Derivative forms include Pero, Pejo, Pera, Perica, Petrica, Periša. Feminine equivalent is Petra. People mononymously known as Petar include: Petar I of Bulgaria (r. 927-969), Emperor (Tsar) of Bulgaria. Petar I Petrović-Njegoš (1747–1830), Montenegrin ruler, metropolitan and saint. Peter I of Serbia (1844–1921), Serbian king.
https://en.wikipedia.org/wiki/Petar