In the Odyssey Odysseus's dog (Argos) is old and weak but thrilled when he recognizes his master before dying peacefully. I'm not aware of any other text where that trope of the loyal dog appears earlier and I hope I see it in Nolan's adaptation and I hope it hits just as hard as when I first read that poem years ago. My second favorite example of that archetype is a certain scene from Robin Hobb's Assassin's Apprentice but I won't say anything else in case someone wants to drop what they're doing and read the first book in a trilogy which kicks off a 16 book fantasy series.