John IV Lascaris was only a boy of 8 years when he was elevated as emperor of the Nicaean Empire in 1258 on the death of his father Theodore II Lascaris. He was the last of the Lascaris emperors that had done much to restore the Byzantine Empire after the capture of Constantinople by the Fourth Crusade in 1204. His regent was Michael Palaeologus, who later made himself co-emperor as Michael VIII. Upon Michael's conquest of Constantinople in 1261, John was ordered blinded, thus making him ineligible to serve as emperor, then imprisoned in a castle on the Sea of Marmara. He is recorded as having acknowledged Andronicus II as emperor in 1290.

Preceded by: Theodore II Lascaris

Byzantine Emperor in exile in the Empire of Nicaea

Succeeded by: Michael VIII Palaeologus