Hesiod gives the monster an early place in Greek genealogy under the name Phix, calling her a destruction to the Cadmeans. Orthrus is named as the father, while the preceding feminine pronoun has generated a long-standing textual problem. Many scholars take the mother to be the immediately preceding Chimera; other ancient and modern readers take it to refer back to Echidna. The Hesiodic genealogy should therefore be described as uncertain rather than simplified.

Pseudo-Apollodorus offers a clearer but different version. Hera sends the Sphinx against Thebes; her parents are Typhon and Echidna; she has a woman's face, lion's body and feet, and bird's wings; and she learns her riddle from the Muses. She sits on Mount Phicium and kills Thebans who cannot solve the question.

The best-known wording asks what has one voice and becomes four-footed, two-footed and three-footed. Oedipus answers that the creature is a human being: an infant crawls on four limbs, an adult walks on two legs and an elderly person uses a staff as a third support. Apollodorus and later sources preserve this wording. Sophocles's Oedipus Tyrannus repeatedly recalls the victory over the Sphinx but never states the riddle in full.

Ancient writers also disagree about the victims and consequences. Apollodorus says the Sphinx eventually takes Haemon, son of Creon, although Sophocles preserves a different Haemon who survives into the Antigone story. Such contradictions show that the Theban cycle was never one perfectly harmonised biography.

After Oedipus gives the correct answer, Apollodorus says the Sphinx throws herself from the citadel, while Diodorus makes her leap from a precipice. Other local and rationalised stories let Oedipus defeat her by force or turn her into a human raider or keeper of a royal secret. The suicide after the riddle remains the dominant literary image, but it is not the only ancient ending.

Greek sphinx imagery is older and broader than the Oedipus story. Sphinxes appear as funerary, protective and decorative beings long before every image can be tied to the Theban riddle. The famous Naxian Sphinx at Delphi, for example, was a monumental dedication rather than an illustration of Oedipus.

The Greek and Egyptian sphinx traditions should therefore remain separate records. The Egyptian sphinx is normally male, wingless and associated with royal or solar guardianship. The Greek Sphinx is female, winged and destructive in the Oedipus cycle. The shared modern name reflects later Greek naming and cross-cultural reception, not one identical creature moving unchanged between the two traditions.