Andronikos I Komnenos (Greek: Ανδρόνικος Αʹ Κομνηνός), usually Latinized as Andronicus I Comnenus, was Byzantine Emperor from 1183 to 1185. He was the son of Isaac Komnenos and the grandson of the emperor Alexios I.
In 1180 the Emperor Manuel died and was succeeded by his ten-year-old son Alexios II, who was under the guardianship of his mother, Empress Maria. Her Latin origins and culture led to creeping resentment from her Greek subjects. They had felt insulted by the Western tastes of Manuel, and being ruled by his Western wife built tensions to an explosion of rioting that almost became a full civil war. This gave Andronikos the opportunity to seize the crown for himself, leaving his retirement in 1182 and marching to Constantinople with an army that (according to non-Byzantine sources) included Muslim contingents. The defection of the commander of the Byzantine navy, megas doux Andronikos Kontostephanos, and the general Andronikos Angelos, played a key role in allowing the rebellious forces to enter Constantinople.
The arrival of Andronikos Komnenos was soon followed by a massacre of the city's Latin inhabitants, who virtually controlled its economy, resulting in the deaths of thousands of Westerners. He was believed to have arranged the poisoning of Alexios II's elder sister Maria the Porphyrogenita and her husband Renier of Montferrat.
Andronikos seems to have resolved to exterminate the aristocracy, and his plans were nearly successful. But on September 11, 1185, during his absence from the capital Stephen Hagiochristophorites, his lieutenant, moved to arrest Isaac Angelos, whose loyalty was suspect. Isaac killed Hagiochristophorites and took refuge in the church of Hagia Sophia. He appealed to the populace, and a tumult arose that spread rapidly over the whole city.
When Andronikos arrived he found that Isaac had been proclaimed Emperor. The deposed Emperor attempted to escape in a boat with his wife Agnes and his mistress, but they were captured and he was brutally killed.
Andronikos I was the last of the Komnenoi to rule Constantinople, although his grandsons Alexios and David founded the Empire of Trebizond in 1204. Their branch of the dynasty was known as the "Great Komnenoi" (Megaskomnenoi).