Alcaeus (Alkaios, Ancient Greek: Ἀλκαῖος) of Mytilene (c. 620 – 6th century BC), Ancient Greek lyric poet who supposedly invented the Alcaic verse. He was included in the canonical list of nine lyric poets by the scholars of Hellenistic Alexandria. He was an older contemporary and an alleged lover of Sappho, with whom he may have exchanged poems. He was born into the aristocratic governing class of Mytilene, the main city of Lesbos, where he was involved in political disputes and feuds.

The broad outlines of the poet's life are well known. He was born into the aristocratic, warrior class that dominated Mytilene, the strongest city-state on the island of Lesbos and, by the end of the seventh century BC, the most influential of all the Asiatic Greek cities, with a strong navy and colonies securing its trade-routes in the Hellespont. The city had long been ruled by kings born to the Penthilid clan but, during the poet's life, the Penthilids were a spent force and rival aristocrats and their factions contended with each other for supreme power. Alcaeus and his older brothers were passionately involved in the struggle but experienced little success. Their political adventures can be understood in terms of three tyrants who came and went in succession: