In Greek mythology, Argos was Odysseus' faithful dog. He waited for his master's return to Ithaca for over a decade while most presumed Odysseus dead. He was the first to recognize the King returning from the Trojan War, even though Odysseus was disguised as a beggar to discover what was going on in his palace during his absence. It was said that as soon as Argos recognized his master, he dropped his ears and did his best to wag his tail. Having fulfilled his destiny of faith by laying his eyes upon his master once more, he released a final wimper and died.

Homer, Odyssey , Book 17:

And so these two men    
talked to each other about these things.  Then a dog
lying there raised its head and pricked up its ears.
It was Argus, brave Odysseus' hunting dog,
whom he himself had raised many years ago.
But before he could enjoy being with his dog,
he left for sacred Troy.  In earlier days, young men
would take the dog to hunt wild goats, deer, and rabbits, 
but now, with his master gone, he lay neglected
in the piles of dung left there by mules and cattle,
heaped up before the doors until Odysseus' servants
took it as manure for some large field.  Argus lay there,  
covered in fleas.  Then, when he saw Odysseus,
who was coming closer, Argus wagged his tail
and dropped his ears.  But he no longer had the strength
to approach his master.  Odysseus looked away
and brushed aside a tear—he did so casually 
to hide it from Eumaeus.  Then he questioned him:  
"Eumaeus, it's strange this dog is lying here,
in the dung.  He has a handsome body.
I'm not sure if his speed once matched his looks
or if he's like those table dogs men have,
ones their masters raise and keep for show."  
Then, swineherd Eumaeus, you answered him and said:
"Yes, this dog belongs to a man who died
somewhere far away.  If he had the form
and acted as he did when Odysseus
left him and went to Troy, you'd quickly see  
his speed and strength, and then you'd be amazed.
No wild animal he chased escaped him
in deep thick woods, and he could track a scent.
He's in a bad way now.  His master's dead
in some foreign land, and careless women
don't look after him.  For when their masters   
no longer exercise their power, then slaves
have no desire to do their proper work.
Far-seeing Zeus takes half the value of a man
the day he's taken and becomes a slave." 
This said, Eumaeus went inside the stately palace,
going straight into the hall to join the noble suitors.
But once he'd seen Odysseus after nineteen years,
the dark finality of death at once seized Argus.