dynasty of Bulgarian tsars during the second Bulgarian empire (1187–1280). It was founded by the boyars Asen and Peter, who led an uprising in 1185–87 against Byzantine domination of Bulgaria. Asen I (1187–96) and his brother and co-ruler Peter I (1187–97) were followed by Kaloian (1197–1207), Boril (1207–18), Ivan Asen II (1218–41), Kaliman I (1241–46), Michael I Asen (1246–56), Kaliman II (1256–57), Constantine Asen the Quiet (1257–77), Michael II Asen (1277–79), and Ivan Asen III (1279–80). The last Asen, whose reign was characterized by increased fragmentation in the feudal order, fled to Constantinople and thereby brought the dynasty to an end.