Mnemosyne (Greek Mνημοσύνη, or /nɪˈmɒsəni/) (sometimes confused with Mneme or compared with Memoria) was the personification of memory in Greek mythology. This titaness was the daughter of Gaia and Uranus and the mother of the Muses by Zeus.
In Hesiod's Theogony, kings and poets receive their powers of authoritative speech from their possession of Mnemosyne and their special relationship with the Muses.
Zeus and Mnemosyne slept together for nine consecutive nights and thereby created the nine Muses. Mnemosyne also presided over a pool in Hades, counterpart to the river Lethe, according to a series of 4th century BC Greek funerary inscriptions in dactylic hexameter. Dead souls drank from Lethe so they would not remember their past lives when reincarnated. Initiates were encouraged to drink from the river Mnemosyne when they died, instead of Lethe. These inscriptions may have been connected with Orphic poetry (see Zuntz, 1971).
Similarly, those who wished to consult the oracle of Trophonius in Boeotia were made to drink alternately from two springs called "Lethe" and "Mnemosyne". An analogous setup is described in the Myth of Er at the end of Plato's Republic.
In the Xena: Warrior Princess episode Forget Me Not (Season 3, Episode 14] the character of Gabrielle goes to the temple of Mnemosyne to try and forget her painful memories. (Throughout the episode it is mispronounced in a fashion that rhymes with limousine.)
In Xanadu (film), Mnemosyne is the (unnamed) mother of the Nine Muses, including Kira, the heroine.
In the fifth arc of Sailor Moon (manga) Sailor Mnemosyne and Sailor Lethe are twins being forced to work for Shadow Galactica. When Sailor Lethe attacks Usagi in the River of Oblivion, Sailor Mnemosyne is the one who stops Sailor Lethe from killing her.