Themistoclea (/ˌθɛmɪstəˈkliːə/; Greek: Θεμιστόκλεια Themistokleia; also Aristoclea (/ˌærɪstəˈkliːə/; Ἀριστοκλεία Aristokleia), Theoclea (/ˌθiːəˈkliːə/; Θεοκλεία Theokleia); fl. 6th century BCE) was a priestess at Delphi.
According to surviving sources Themistoclea was Pythagoras’ teacher.
In the biography of Pythagoras in his Lives and Opinions of Eminent Philosophers, Diogenes Laërtius (3rd century CE) cites the statement of Aristoxenus (4th century BCE) that Themistoclea taught Pythagoras his moral doctrines:
Aristoxenus says that Pythagoras got most of his moral doctrines from the Delphic priestess Themistoclea.
Porphyry (233–305 CE) calls her Aristoclea (Aristokleia), although there is little doubt that he is referring to the same person. Porphyry repeats the claim that she was the teacher of Pythagoras:
He (Pythagoras) taught much else, which he claimed to have learned from Aristoclea at Delphi.
The 10th-century Suda encyclopedia calls her Theoclea (Theokleia) and states that she was the sister of Pythagoras, but this information probably arises from a corruption and misunderstanding of the passage in Diogenes Laertius.