TITHONUS

a son of Laomedon, and brother of Priam or according to others a brother of Laomedon. Others, again, call him a son of Cephalus and Eos.

By the prayers of Eos who loved him he obtained from the immortal gods immortality, but not eternal youth, in consequence of which he completely shrunk together in his old age, whence an old decrepit man was proverbially called Tithonus. (Theogony of Hesiod 984)