Odysseus's loyal dog who recognizes him is Argos. In Homer's Odyssey, Argos sees his master return to Ithaca disguised as a beggar after twenty years away at the Trojan War and on his travels.
Argos has been neglected during Odysseus's absence. He lies weak and covered with fleas near a dung heap, while the household's suitors occupy the palace. Although the disguised Odysseus cannot openly acknowledge him, Argos recognizes him immediately by sight, scent, or memory.
The reunion is deliberately brief and poignant: Argos lifts his ears and wags his tail, then dies after confirming that his master has come home. Odysseus secretly wipes away a tear so that his identity will not be exposed. The dog therefore symbolizes loyalty and the long passage of time.
A common mix-up is with Cerberus, the many-headed guard dog of the Underworld, or with Orthrus, the two-headed dog of Geryon. Neither belongs to Odysseus's household; Argos is the faithful dog in the Odyssey.