Owners: 'The Hulk,' 173-lb pit bull, is playful and sweet

CARROLL, NH -- A 173-pound pit bull named "The Hulk" stands as tall as his owner when lurching on his hind legs.

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Hulk is the family dog of Marlon and Lisa Grennan. They raised the pit bull after was he born in September 2013. The couple runs a dog-training company called Dark Dynasty K9s.

The Grennans say he has a great relationship with their 3-year-old son, Jordan, calling him the "ultimate babysitter."

"He's a wonderful, excellently trained dog," Grennan told ABC News. "He plays with my kid, he's great with the family and he's so, so sweet."

The couple's company has several focuses for their training the dogs, including "Security Dogs and Obedience Training."

"I breed my dogs for size," Dark Dynasty owner Marlon Grennan told The Huffington Post.

Critics of the Grennan's practice say breeders should not breed pit bulls due to their historically aggressive nature.

Grennan tells the Huffington Post that he is very careful about who he allows to purchase his pit bulls. He also takes in rescue dogs and is working to start his own pit bull rescue program.

Hulk has gotten quite a bit of attention online, and Grennan hopes this will help the image of all pit bulls.

"My hope is that we can stop ignorance and change people's minds about pit bulls in a positive way with all this attention," he told ABC News.