From which culture was this pet mummified to meet his master in the afterlife?

This culture considered certain individual animals to be living manifestations of a god.

Those individuals were duly mummifed when they died and buried for eternal life, then replaced by another single living manifestation.

During the first millennium BC, many multiples of animals associated with certain gods were specially raised in temple precincts as simultaneous avatars of that god and then mummified in large contingents and deposited in catacombs for eternal life.

Hundreds of thousands of often elaborately prepared animal mummies have been found in catacombs and other locales.

Answer:An Egyptian mummy containing the remains of a dog. 400-100 BCE, Kharga Oasis, el-Deir. (Metropolitan Museum of Art, New York)

Text excerpted from these sources:

https://www.ancient.eu/image/6417/egyptian-dog-mummy/

https://www.metmuseum.org/art/collection/search/552442