Just as the characters in HBO's smash hit "Game of Thrones" have evolved over the past three seasons, so too have the animals portraying the ancient dire wolves. The creatures have morphed from live animals -- a breed known as the Northern Inuit dog -- to computer-generated images that are bigger, scarier and wolfier than ever.

In "Game of Thrones," a tribe of ancient people encounter a dire wolf mother dead near her surviving cubs. Tribal children are given a cub to raise and learn about elements of honor and sacrifice needed to claim the king's throne. "Game of Thrones" is based on a book series by George R.R. Martin.

The real dire wolf -- canis dirus -- lived across North and South America 10,000 years ago and were about 25 percent bigger than modern gray wolf, weighing up to 175 pounds, according to the San Diego Zoo.

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The first two seasons used dogs bred by Julie Kelham, founder of the Northern Inuit Society in the United Kingdom.

"I think the real dogs are better," said Kelham, who helped develop the breed 25 years ago. "They were supposed to be dire wolves, which were a giant thing, but the Northern Inuits couldn’t measure up to the size of a dire wolf."

Kelham said the Northern Inuit dogs originally had some traces of wolf in their bloodline, but that it has been bred out over the generations as they have been mixed with other northern dogs such as huskies and malamutes.

"They are very, very docile," Kelham said. "They don't make good guard dogs. They are great with kids, great with other dogs."

Lady (Zunni) in the show's first seasonHBO

During the first two seasons of Game of Thrones, live dogs were shot against a green screen that allowed producers to add in visual effects behind them, as well as expand their size and smooth out the edges, according to Jason Zimmerman, creative director and visual effects supervisor at Pixomondo, a Burbank, Calif., studio. Pixomondo created the dire wolves in season 2 and is responsible for the show’s dragons as well.

"You can't beat the real thing photographically," Zimmerman said. "You are looking at something that doesn’t trick the eye because it is a real creature."

During Season 3, which began last month, the animals have become much bigger as the storyline has progressed and the animals have aged.

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"They are now pretty much all CGI (computer generated images)," said Mara Mikialian, an HBO spokeswoman.

Mikialian wouldn't discuss the details of how the new dire wolves are created, but Pixomondo's Zimmerman said it likely is an expensive and time-consuming effort.

"To do that in CGI requires quite a bit of heavy lifting," he said. "It takes a little bit of time to model the performance. For something like Game of Thrones, you need to turn it around fairly quickly. Conversations about time and money come into play."

A group of dire wolf lovers in Oregon is trying to recreate the look of the original dire wolf by breeding characteristics into the American Alsatian dog. The group's site says some individuals have reached 140 pounds, but are still far cry from the massive creatures that roamed prehistoric North America, and now HBO on Sunday nights.