(CNN) Casper has spent his life, all 63 dog-years of it, serving others.

With every tail wag and wet-nose kiss, he has spread love and happiness in a place that can feel desperate: Children's Healthcare of Atlanta, where kids are often confined to their hospital rooms for months on end.

Though their families try to stay optimistic, they are scared. The doctors and nurses do their best to remain upbeat, but even they too grow weary sometimes, which is when Casper comes in.

But in November, Lisa Kinsel, Casper's handler, noticed something wrong when he was at home: His left side was weak, and he couldn't stand or walk properly.

Casper had suffered a stroke from a blood clot in his brain. Everyone's favorite therapy dog was in need of therapy himself.

Unconditional love

Thoughout his life, Casper had loved unconditionally; he's a dog, so that's what he does. Visiting patients in their rooms on his daily rounds, he can put a smile on the face of almost everyone he meets.

There's something magical about Casper in particular, which is why, despite a fleet of service pups at the hospital, he is the star.

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"He's like a big sponge," Kinsel said. "I think that's what makes him work so well with the patients. He knows that the child is maybe anxious, maybe in pain, and so when he's there to help them, he sort of soaks that all in. And it helps eliminate their stress."

Casper began his therapy work in 2009, and whenever his service vest goes on, he knows it's time to do his job. A full-time employee at Children's Healthcare, he even has his own badge.

Small plush versions of Casper, complete with green vest, are clutched in little hands throughout the hospital. He's an integral part of the community, and the recovery, for sick and injured children in their hospital beds.

He's also important to the staff.

"That was one of the things we really didn't think about when we started this," Kinsel said. "It was all about the patients and families. And then more and more, we were finding that the staff were calling and saying, 'We've had a really rough day in Intensive Care today. Will you please bring him up? Because the staff need to see him.' "

Kinsel added that the hospital is not an easy place to be sometimes, and the staff recognized how much Casper was doing for them.

But, for all he's done, Casper now needs some love and care in return.

Recovering from a stroke

Since December. Casper has been doing physical therapy with Dr. Kimberly Neff at Georgia Veterinary Rehab. "We don't know what predisposes dogs to strokes, just like we don't know for humans," Neff said. "Of all the things neurologists see, it's not that common in dogs."

Casper has unconditional love for the patients at Children's Healthcare of Atlanta.

Casper's stroke created a deficit on his left side, which was weakened, leaving him unsure where his front left paw was hitting. Neff worked with him every week to regain his muscle strength.

Part of Casper's therapy included an underwater treadmill, providing exercise without putting too much pressure on his joints. A swipe of tasty peanut butter on the glass in front of him kept him motivated.

Kinsel senses that Casper feels lost without his hospital work, and she holds out hope that he can return to work soon. As he's grown stronger, she has taken him for some short visits to the hospital: The doctors, nurses and administrators need their dose of Casper love just as much as he needs to give it to them.

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On one visit, when he was too weak to walk in, his friends in the radiology department brought out his usual treat of cooked egg yolks to the curb. Casper joyfully gobbled up his yolks, back where he belonged, even if just for a short time.

With his condition improving, Casper was recently able to celebrate his 9th birthday with a party at Children's Healthcare. Numerous patients and hospital staff members turned out to sing to him. He made his way around the lobby, greeting each and every person. Casper was feeling the love, and it helped him progress through his therapy.

In late January, Neff graduated Casper from physical therapy after he made a full recovery.

"Physically, you'd never know anything happened," Neff said. "Dogs really are incredible."