Ano kaya back story nung aso?
Lucky the Pizza Dog is the name of the Golden Retriever of Kate and Clint.
I dig some more and this actually makes sense since I saw the same Golden Retriever in Guardians of the Galaxy scenes:
Though Lucky is already a significant part of Hawkeye, the dog may have a deeper purpose in the MCU. According to a fan theory (via Reddit), Lucky is secretly Cosmo the Spacedog. Cosmo previously appeared in the Guardians of the Galaxy films, where he was initially part of The Collector's (Benicio Del Toro) collection and played by a dog named Fred. However, Howard the Duck (Seth Green), who was also part of the collection, winds up at the battle against Thanos (Josh Brolin) in Avengers: Endgame. Therefore, Cosmo could be more than an Easter egg. The dog also could've been part of the battle at the Avengers Compound. And since the plot of Hawkeye involves stolen items from the Avengers Compound getting sold at a black-market auction in New York, it makes sense that Cosmo could've tagged along for a ride from the Avengers' headquarters too. There, he meets Kate Bishop and becomes Lucky.
The theory has enough evidence to work. Cosmo has telepathic powers in Marvel's comics, and the dog seems to have an odd understanding of both Clint Barton and Kate Bishop. Additionally, while the comics show the Tracksuit Mafia originally owned Lucky, the Hawkeye series just has the dog show up out of nowhere to protect the items from the Avengers Compound as a Tracksuit Mafia member tries to steal them. Kate Bishop also wears a shirt acknowledging Laika, a dog the Soviet Union sent into space. In Marvel's comics, Cosmo obtains powers after being sent into space.
https://youtu.be/r30nn9RqlvE