Alexios III Angelos (Medieval Greek: Ἀλέξιος Ἄγγελος, romanized: Aléxios Ángelos; c. 1153 – 1211), Latinized as Alexius III Angelus, was Byzantine Emperor from March 1195 to 17/18 July 1203. He reigned under the name Alexios Komnenos (Ἀλέξιος Κομνηνός; Aléxios Komnēnós) associating himself with the Komnenos dynasty (from which he was descended cognatically).

A member of the extended imperial family, Alexios came to the throne after deposing, blinding and imprisoning his younger brother Isaac II Angelos. The most significant event of his reign was the attack of the Fourth Crusade on Constantinople in 1203, on behalf of Alexios IV Angelos.

Alexios III took over the defence of the city, which he mismanaged, and then fled the city at night with one of his three daughters. From Adrianople, and then Mosynopolis, he attempted unsuccessfully to rally his supporters, only to end up a captive of Marquis Boniface I of Montferrat. 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.