Alexios was the elder brother of the emperor Isaakios II (1185–1195), who he deposed and blinded. Although he had some military success against the Second Bulgarian Emperor, established during the reign of Isaakios II, provincial leaders attempted to establish independent territories. This led to a splintering of the empire, with outlying provinces falling away from central control. The culmination of this process can be seen following the sack of Constantinople in 1204 and the loss of all central government, when the empire shattered, never to be reconstituted. Even closer to home in Constantinople, the ineffectiveness, and occasional outright tyranny, of Alexios's rule left the capital unready to confront the challenge of the Fourth Crusade. Soon after the crusader army and Venetian fleet appeared before Constantinople in 1203 Alexios fled the city, leaving the defense of Constantinople to his nephew Alexios IV and his blind brother Isaakios.
Initially Alexios followed many of the design trends of the Komnenian emperors. His first seals depict an enthroned Christ on the obverse and the emperor, identified by his family name of Angelos, on the reverse. His second type of seal (see top) is completely different. For the first time on iconic imperial seals since the sixth century, the religious figure depicted is neither the Mother of God nor Christ, but is instead a saint: St. Constantine, the great fourth-century emperor and founder of Constantinople. On coins, by contrast, Alexios appears with the saint on the reverse, and they hold between them a patriarchal cross on a long shaft, while the obverse depicts Christ standing on a dais. Also notable on this second design is a switch in family name. The emperor is no longer Alexios Angelos, but Alexios Komnenos. By adopting the name of the dynasty established by Alexios I in 1081, Alexios III was linking himself to a glorious imperial past, and a century of success. His choice of the name Komnenos also demonstrates the fluidity with which family names could be switched or chosen by the aristocracy of this period, who would often look back along their pedigree and select the name which seemed most appropriate or useful for them. This trend can be seen on the seals of the emperors of Nicaea and Thessalonike in the decades after Alexios III. For more on the seals of Alexios III, see his entry in the section Interlopers and Usurpers.