Its superb sense of smell ensures that this Pokémon won't forget any scent, no matter what. It uses its sense of smell to detect the emotions of others.
(From Bulbapedia) Growlithe is a quadruped, canine Pokémon. It has orange fur with black stripes along its back and legs. The fur on its muzzle, chest, belly, and tail is cream-colored, as well as an additional tuft of fur on top of its head. Growlithe's coat is noticeably longer on its chest and tail. It has gray eyes, a black nose, and large, round ears. Its forepaws have two visible claws, while its hind paws have three toes each. Each paw has a brown pad.
Growlithe is a friendly and loyal Pokémon that will fearlessly defend its Trainer and territory from harm, even against larger, stronger enemies. It will fiercely bark at, bite, and chase away any perceived threat, including those who suddenly approach its Trainer. Otherwise, this obedient Pokémon will wait motionlessly until given an order. Growlithe also has a powerful olfactory sense. If it detects an unknown smell in its territory, it roars to flush out the intruder. It is able to smell the emotions of others, and never forgets a scent. However, strong, unpleasant smells can disable its sense of smell for short periods, as seen in the anime. Growlithe can be commonly found in grassy plains.
(From Bulbapedia) Growlithe is most likely based on Japanese dog statues called shisa. They may also originate from Chinese shī or Japanese komainu, which are guardian statues that resemble lions, with traits of tigers and dogs. They are incorrectly called "Foo dogs" in the West. Both shisa and shī statues alike are often found in pairs, believed to invite good luck, and used as guardians, which may have inspired Growlithe's protective nature.
(From Bulbapedia) Growlithe may be a combination of growl and lithe.