He became a successful general in the Nicaean Empire and in 1258 became regent for, and soon co-ruler with, the eight-year-old Emperor John IV Lascaris. Later he had John IV blinded and imprisoned, thus becoming sole ruler of Nicaea. In 1261 he became Emperor of Constantinople, in the process becoming embroiled with the papacy and Charles of Anjou, who aimed to re-establish the Latin Empire with himself as emperor. 
The forced reunion of the Orthodox Church with Rome aroused great discontent among his subjects but warded off attacks until 1281. The even more hostile Pope Martin IV (1281-1285) proclaimed a crusade against him, but Michael VIII incited discontent in Sicily, which was 
invaded by his allies the Aragonese, thereby ending Charles of Anjou's threatening ambitions. 

Source: Leo van de Pas