Baybars (r.1260-1277) is account the real founder oft the bhari Mamluk sultanate. After playing a decicive role in the resistance agians the crusaders in the Mansura's battle en 1250, Baybars distinguishes himself besides sultan Qutuz at tjhe Mamluk victory of the Mongol at ‘Aun Jâlût in September 1260. But Baybars ascends to power at a time when a new ideology gain in importance throughout the dâr al-islâm. Chinggis Khans's successors claime for themselves the imperial good fortune bestrowed on the royal kindred by tjr eternal sky. Indeed, brought as a slave, Baybars has nothing to the equal this Mongols nasab. Futhermore, he escends to power after, if not committing, at least instigating a double regicide: in 1250, the murder of Türan-Shâh, his master's son and legitime heir and then in 1260 the assasination of Mamluk sultan Qutuz by a conspiracy of emirs he is a party to. The aim of this paper is to show the means used by Baybars himself to ground his legitimacy on islam. The author uses much types of sources (biographies, chronicles, monumental epigraphy and apocalyptical literature). His legitimacy reposed of two themes, either putting him with the qualities of ideal musulman ruler, or emphasing his eschatological role. He is indeeed described in the apocalyptical literature as the “last emperor”, the victorious sovereign who is to save his religious community by purifing from its sins. Barbars' legitimacy is build in contrast to the ideal ruler's, but he's given a role whose eschatological scope is in the line with the meaning of the title of “Alexander of time” he receives in monumental epigraphy.