When Speranza Animal Rescue got a call telling them that an especially irritable bulldog was headed their way, staff members weren’t sure who to expect.

In sauntered Frank, and rescue staff took one look at his resting grumpy face and knew they might have a challenge on their hands.

Frank’s demeanor matched his frown — he often acted aggressively and unpredictably. Regardless, staff members were happy to show Frank the love and compassion he so clearly had been missing.

“He was found as a stray and he was less than friendly,” the rescue wrote in a Facebook post. “His permanent RBF was accompanied by low growls and snarls … This little gremlin is short in stature, but has an attitude for days. But we are so in love already.”

Though they were initially skeptical, empathetic rescue staff quickly grew fond of the spirited little guy.

“Some of the volunteers thought, ‘Oh no, another big attitude,’ when they heard about Frank coming,” rescue representative Janine Guido told The Dodo. “[But then they] fell head over heels.”

Using positive reinforcement, rescue staff patiently began to teach Frank manners — like how to ask for what he wanted without showing aggression, and how to walk on a leash. Days went by, and Frank began to trust his new friends and even have fun with them. It wasn’t long before his frown vanished to reveal the sweetest smile.

Guido is thrilled with Frank’s transformation so far.

“Frankfort is making good progress within the rescue and with the volunteers!” Guido said. “He doesn’t greet people with growls anymore, which is a win for all of us.”

Soon, Frank will head to a foster family, where he’ll continue to learn how to be a good boy. Once Frank is ready, he will be up for adoption and will find his permanent home.

In the meantime, he’ll get to do all his favorite activities — like playing with his toys and going on long walks.

Thanks to the patience and determination of the dog lovers who believe in him, this once-grumpy boy is going to live the happy life he deserves.