Ivan Asen II of Bulgaria
Ivan Asen II, also known as John Asen II or John Asan II (Bulgarian: Иван Асен II, [iˈvan ɐˈsɛn ˈftɔri]; 1190s – May/June 1241), was Emperor (Tsar) of Bulgaria from 1218 to 1241. He was still a child when his father Ivan Asen I – one of the founders of the Second Bulgarian Empire – was killed in 1196. His supporters tried to secure the throne for him after his uncle, Kaloyan, was murdered in 1207, but Kaloyan's other nephew, Boril, overcame them. Ivan Asen fled from Bulgaria and settled in the Rus' principalities.

Boril could never strengthen his rule which enabled Ivan Asen to muster an army and return to Bulgaria. He captured Tarnovo and blinded Boril in 1218. Initially, he supported the full communion of the Bulgarian Church with the Papacy and concluded alliances with the neighboring Catholic powers, Hungary and the Latin Empire of Constantinople. He tried to achieve the regency for the 11-year-old Latin Emperor, Baldwin II, after 1228, but the Latin aristocrats did not support Ivan Asen. He inflicted a crushing defeat on Theodore Komnenos Doukas of the Empire of Thessalonica, in the Battle of Klokotnitsa in 1230. Theodore's empire soon collapsed and Ivan Asen conquered large territories in Macedonia, Thessaly and Thrace.

The control of the trade on the Via Egnatia enabled Ivan Asen to implement an ambitious building program in Tarnovo and struck gold coins in his new mint in Ohrid. He started negotiations about the return of the Bulgarian Church to Orthodoxy after the barons of the Latin Empire had elected John of Brienne regent for Baldwin II in 1229. Ivan Asen and the Emperor of Nicaea, John III Vatatzes, concluded an alliance against the Latin Empire at their meeting in 1235. During the same conference, the rank of patriarch was granted to the head of the Bulgarian Church in token of its autocephaly (independence). Ivan Asen and Vatatzes joined their forces in attacking Constantinople, but the former realized that Vatatzes could primarily take advantage of the fall of the Latin Empire and broke off his alliance with Nicaea in 1237. After the Mongols invaded the Pontic steppes, several Cuman groups fled to Bulgaria.