In Greek mythology, the name Astacus (Ancient Greek: Ἄστακος) may refer to:

• Astacus of Thebes, a descendant of the Spartoi, and the eponym of the city Astacus, characterized as "a noble and proud man".^[1] One of his sons, Melanippus, was one of the principal defenders of Thebes in the war of the Seven against Thebes and fell against Tydeus.^[2] His other three sons, Ismarus, Leades, and Amphidicus (or Asphodicus), were credited with killing Hippomedon, Eteoclus and Parthenopaeus respectively.^[3] Yet other two sons of his, Erithelas and Lobes, were said to have founded Hypoplacian Thebes.^[4]
• Astacus, a son of Poseidon and the nymph Olbia, eponymous founder of Astacus, Bithynia.^[5]
• Astacus, a son of Hermes and (?) Astabe, a daughter of Peneus; he was father of Iocles (or Oicles?) and through him grandfather of Hipponous.^[6]