Stimpy, a 6-year-old blue teacup Chihuahua, was tough enough to summit a fourteener, float the Arkansas River and Ride The Rockies in the saddlebag of his owner's bike.

But the 2.6-pound pooch couldn't survive being struck by a bicycle in Washington Park Wednesday morning.

Hank Martin had run around the park with Stimpy on his leash and had just let the tiny dog off his lead for a little free play when he heard a yelp.

The dog had darted in front of a bicyclist riding in the crowded park. The bicyclist stopped to help.

"I thought he had just been dinged," but when Martin picked Stimpy up, the dog's body went limp.

Martin rushed the dog to the veterinarian who concluded Stimpy's lungs were severely bruised in the collision and he suffocated.

Martin, who moved to Denver's Washington Park neighborhood from Louisville two weeks ago, said the dog was far more popular than he was.

"If I went into a store, it wasn't 'Hi Hank,' it was 'STIMPY!' I took him to restaurants and pubs and he would poke his head out of the backpack and people would say, 'We don't allow dogs, but he can stay,' " Martin said.

Martin said he's heartbroken about what happened to his beloved dog, "he was the joy of my life."

But Martin also acknowledged the risk of letting the dog off his leash.

"I have to tell everybody watch your dog in Washington Park and bicyclists, watch for dogs," he said. "He could have been on the leash when it happened."

Denver Parks and Recreation spokesman Jeff Green said Wednesday that dogs are only allowed off leash in the city's designated dog parks.

"In a regular park, like Washington Park, dogs must be on a leash and in control by their owner or the person that brought them to the park," Green said.