the personification of oblivion, is called by Hesiod (Theogony of Hesiod 227) a daughter of Strife.
Lethe is one of the rivers of Hades. Drinking from the river Lethe caused complete forgetfulness. Some ancient Greeks believed that souls were made to drink from the river before being reincarnated, so they would not remember their past lives.
(ll. 211-225) And Night bare hateful Doom and black Fate and Death, and she bare Sleep and the tribe of Dreams. And again the goddess murky Night, though she lay with none, bare Blame and painful Woe, and the Hesperides who guard the rich, golden apples and the trees bearing fruit beyond glorious Ocean. Also she bare the Destinies and ruthless avenging Fates, Clotho and Lachesis and Atropos, who give men at their birth both evil and good to have, and they pursue the transgressions of men and of gods: and these goddesses never cease from their dread anger until they punish the sinner with a sore penalty. Also deadly Night bare Nemesis (Indignation) to afflict mortal men, and after her, Deceit and Friendship and hateful Age and hard-hearted Strife.
(ll. 226-232) But abhorred Strife bare painful Toil and Forgetfulness and Famine and tearful Sorrows, Fightings also, Battles, Murders, Manslaughters, Quarrels, Lying Words, Disputes, Lawlessness and Ruin, all of one nature, and Oath who most troubles men upon earth when anyone wilfully swears a false oath.
Lethe was also a naiad, the daughter of Eris ('Strife' in
Hesiod's Theogony). The naiad Lethe is probably a separate
personification of forgetfulness rather than a reference to the
river which bears her name.