A member of the extended imperial family, Alexios came to the throne after deposing, blinding and imprisoning his younger brother Isaac II Angelos.

He was ransomed and sent to Asia Minor where he plotted against his son-in-law Theodore I Laskaris, but was eventually captured and spent his last days confined to the Monastery of Hyakinthos in Nicaea, where he died.

Together with his father and brothers, Alexios had conspired against Emperor Andronikos I Komnenos (c. 1183), and thus he spent several years in exile in Muslim courts, including that of Saladin.

In March 1195 while Isaac II was away hunting in Thrace, Alexios was acclaimed as emperor by the troops with the covert support of his wife Euphrosyne Doukaina Kamatera.

[3] To compensate for this crime and to solidify his position as emperor, Alexios had to scatter money so lavishly as to empty his treasury, and to allow such licence to the officers of the army as to leave the Empire practically defenceless.

The Empress Euphrosyne tried in vain to sustain his credit and his court; Vatatzes, the favourite instrument in her attempts at reform, was assassinated by the emperor's orders.

The Emperor's attempts to bolster the empire's defences by special concessions to pronoiai (notables) in the frontier zone backfired, as the latter increased their regional autonomy.

[4] During the first years of Alexios' reign, relations between Byzantium and Serbia were good, since his daughter Eudokia Angelina was married to Serbian Grand Prince Stefan Nemanjić II, who was granted the title of sebastokrator.

[3] The crusaders, whose objective had been Egypt, were persuaded to set their course for Constantinople, arriving there in June 1203, proclaiming Alexios IV as emperor, and inviting the populace of the capital to depose his uncle.

[citation needed] In July, the crusaders, led by the aged Doge Enrico Dandolo, scaled the walls and took control of a major section of the city.

Alexios III attempted to escape Boniface's "protection" in 1205, seeking shelter with Michael I Komnenos Doukas, the ruler of Epirus.