His father Theodore ruled over the Byzantine successor state of Epirus since 1215, and after the conquest of the Latin Kingdom of Thessalonica in 1224, had founded the Empire of Thessalonica, in rivalry with the other major Byzantine successor state, the Empire of Nicaea in western Asia Minor. By 1230, he seemed poised to recover Constantinople from the Latin Empire and thus restore the Byzantine Empire, but in that year he was defeated and captured at the Battle of Klokotnitsa by Ivan Asen II of Bulgaria, and was blinded after being implicated in a plot against Ivan Asen. In the aftermath of Klokotnitsa, Theodore's empire collapsed: within a few months most of Thrace, Macedonia, and Albania, fell under Bulgarian rule. Theodore's brother Manuel, who managed to escape from Klokotnitsa, now took over the throne in Thessalonica, ruling over a much-reduced domain as a vassal of the Bulgarian ruler. When his sister Irene married Ivan Asen in 1237, Theodore was released from captivity. Theodore made his way back to Thessalonica and overthrew Manuel, but as he was blind, he installed his oldest son John as emperor. In 1244, however, the Nicaean emperor John III Doukas Vatatzes campaigned against Thessalonica, and forced John to recognize his suzerainty and renounce his imperial title, receiving the title of Despot instead.