The Asen dynasty (Bulgarian: Асеневци, Asenevtsi) ruled a medieval Bulgarian state, called in modern historiography the Second Bulgarian Empire, between 1187 and 1256.
The Asen dynasty and the Second Bulgarian Empire rose as the leaders of a rebellion against the Byzantine Empire at the turn of the year 1185/1186 caused by the increase in the Imperial taxes.
Early rulers from the Asen dynasty (particularly Kaloyan) referred to themselves as "Emperors of Bulgarians and Vlachs". Later rulers, especially the successful Ivan Asen II, styled themselves "Tsars (Emperors) of Bulgarians and Greeks".
Some members of the Asen family entered Byzantine service in the thirteenth to fourteenth centuries.The name also occurs as a family name in modern Greek, and could go back to the same name.
Read more about Asen Dynasty: Rulers From The Asen Dynasty, Origins, Name