For those who encountered them on the west end of Pearl Street, Greg Pike and his animals -- dog Booger, cat Kitty and rat Mousie -- are hard to forget.

The creatures bucked stereotypes of animal behavior, and even their basic nature, to band together and form a one-of-a-kind animal pyramid: rat on top of cat on top of dog.

Pike was one of Boulder's best-known buskers, but the act is over.

Booger, 13, died Monday night from kidney and liver failure at a veterinary clinic in his hometown of Telluride, Pike said. He had raised the Rottweiler-Labrador mix from a puppy.

"I think my eyes are drained. It really hurts," he said Tuesday. "She didn't die in pain at all. She passed away in comfort in Telluride, where she loved to be."

Soon after he was given the puppy, he began his dog-cat-rat act on whim, he said. One day in a Telluride park, Pike and some others were discussing the limits of what's possible, and he bet that he could get a dog, cat and rat to get along.

After finding Kitty and her littermates in a box under a house, Pike said he introduced the cat to Booger, who adopted the kitten as though she was her puppy. There have been several Mousies, but Booger and Kitty were inseparable from that point.

"I've never seen her curl up to me this much," Pike said of the cat in the absence of Booger.

Outside of Boulder, Pike took the animals all across the U.S., embarking on a road trip eight years ago, he said, that took him from San Francisco to New York City to Key West, Fla., on a 1939 Allis Chalmers tractor dragging three hand-built trailers.

Spurred on by the sadness he saw in people after 9/11, Pike said he liked the reaction the animals got when they were walking around stacked on one another.

"Everywhere I brought them, they made people smile, and it just made me feel really good inside," Pike said.

Pike said Booger might have been one of the most famous dogs in the world over the last decade, with the dog-cat-rat stack receiving attention from media outlets and the Animal Planet series "Must Love Cats." A YouTube video titled "Dog, Cat and Rat" featuring Pike and his animals has been viewed more than 9.75 million times.

Pike said he plans to work as a ski lift operator in Telluride this winter to raise money for his next adventure. He said he will focus on animals and bringing joy to people, but there will not be another dog-cat-rat act. He said that was a once-in-a-lifetime thing.

Pike said the dog will be cremated, and in the spring he will climb to the top of Gold Hill in Telluride -- her favorite place on Earth -- to spread her ashes.