Petco, founded in 1965 in San Diego, started as a mail-order business providing veterinary supplies before shifting to retail in 1979. This move led to its expansion across the U.S. offering a variety of pet supplies. By the 1990s, Petco became a prominent player in the pet industry and launched its "Think Adoption First" initiative to promote pet adoption. In the 2000s, it embraced e-commerce and expanded services like grooming, training, and veterinary care.