Just after the fall of Constantinople by the Latins in 1204, the grandsons of Andronikos Kommenos, Alexios and David Kommenos, having taken the support of their aunt, the Georgian queen Thamara, captured Trebizond and afterwards established the empire of Trebizond. On the other hand, after the conquest of Constantinople, while Theodoros Laskaris prevailed over İznik, Mikhail Dukas, another representative of Angelos Dynasty, had a sovereign over Epir. The main idea of these states was the restoration of Byzantine Empire in Constantinople. Besides, although it happened to be a limited area around and the vicinity of Trebizond, the kings of the Empire of Trebizond which continued to exist longer than Byzantium Empire, maintained their claims over the imperial crown for itself. In this article, we shall evaluate the legality of the emperors of Trebizond by taking into account Byzantium sources between XIIIth and XVth centuries.