Bertie has been around longer than any of his fellow tenants. He moved in on December 16, 1958, back when "The Donna Reed Show" was on TV and Dwight D. Eisenhower was in the White House.

He's fathered 29 offspring, despite having only two mates.

And oh yeah, Bertie is a hippopotamus at the Denver Zoo. This week (Thursday, to be exact) the zoo will celebrate his 58th birthday.

"He's a star," says zoo veterinarian Diana Boon. "A lot of people come here just to visit him."

In January, Bertie unwittingly became the oldest hippopotamus in North America-and maybe the world- after a hippo named Blackie was euthanized at the Cleveland Metroparks Zoo. Blackie was believed to be 59.

In the wild, hippos can live to be about 30 to 40 years old. In captivity, they generally live another 10 years. Bertie has so far defied those numbers, though his keepers say he's moving a bit slower these days.

"We see geriatric problems, some arthritis in the legs, some stiffness getting up and moving around. He's also got some dental issues," says Boon. "But for his age, he's surprisingly doing very well."

Bertie gets regular medication for his aching joints. He spends a lot of time in the water, which his keepers say helps alleviate the pressure of carrying around a roughly 5,000-pound frame.

Zookeeper Lisa Parrish helps with a daily regimen to clean out the clumps of hay that get stuck in Bertie's mouth, where they could cause sores and lead to infection.

"Open Bertie," Parrish instructs with a hand motion.

Bertie patiently exposes his giant teeth while resting his head at the edge of his outdoor pool, as Parrish uses giant forceps to do the job.

"You don't necessarily want to stick your hands in a hippo's mouth," Parrish says.

When she's done, Parrish grabs a container filled with grain mixed with medicine, tossing the contents into Bertie's mouth.

"You're a good boy Bert," Parrish tells him. "We always wonder if this is going to be his last birthday, but luckily he's been doing really good."

Bertie was a 1,200 pound 2-year-old living at New York's Central Park Zoo in 1958. That year, Denver zoo supporters Arthur and Helen Johnson bought him at an auction for $2,450 plus tax, and arranged to have him shipped to Denver.

One of Bertie's 29 hippo offspring, Mahali, also lives at the Denver Zoo. Parrish says father and his 11-year-old son have to be kept in separate enclosures.

"They do not get along," says Parrish. "Hippos are very territorial."

In the wild, the hippopotamus population has declined about 20 percent in the last decade to around 125,000 to 150,000 individuals, according to the Wildlife Conservation Society. There has been an especially drastic drop in numbers-around 95 percent by WCS estimates- in the Democratic Republic of Congo due to civil war and poaching of ivory teeth and tusks.