He's a proven stud from Cincinnati, having fathered eight children. She's a shy, hand-raised spinster from Dallas, who has little romantic experience but loves to be around others' babies.

Despite their differences, a lot of hope is riding on this newly introduced couple--a pair of gorillas recently brought here to repopulate the Philadelphia Zoo's great ape collection, which was wiped out in a Christmas Eve fire 3 1/2 years ago.

The unlikely pair--Chaka, 14, the authoritative silverback male, and Demba, 29, a temperamental female raised by humans after her mother rejected her--are the centerpieces of the new $24 million primate reserve opening Thursday. The impressive new exhibit, designed to resemble an abandoned timber mill reclaimed by conservationists, is large and bright and the animals are easily viewable--all things the previous primate space was not.

Already, the 11 species of primates have attracted a steady stream of visitors this month during a members-only preview, guests the zoo has needed sorely these past few years as the number of daily visitors and annual memberships dwindled in the aftermath of the fire and the deaths of 23 of the zoo's most popular animals, including gorillas, orangutans, gibbons and lemurs.

Since the December 1995 fire, zoo attendance has dropped from about 1.25 million to 1.1 million visitors annually, said Dell Fioravanti, vice president of marketing. The number of memberships plummeted from a high of about 65,000 in 1994, when the zoo put popular white lion cubs on view, to about 51,000 memberships in each of the last three years.

The drop in visitors was expected. "The primates are the heart of the zoo," explained Alexander "Pete" Hoskins, zoo president.

The fire, caused by faulty installation of heating tape wrapped around pipes, was only the latest--albeit the most tragic and publicized--problem the zoo faced.

The Philadelphia Zoo is the nation's oldest--it will celebrate its 125th anniversary Thursday when the primate reserve officially opens--and it was not aging gracefully. Unlike many other zoos, which Hoskins said are heavily subsidized by local governments, the Philadelphia Zoo relies on gate and concession receipts to meet 85 percent of its annual operating budget.

Capital improvements and exhibit renovations had been put on hold for decades while many other zoos were investing in modern, naturalistic exhibits and creature comforts for visitors. By the early 1990s, the Philadelphia Zoo's accreditation was in jeopardy because its on-site animal hospital wasn't up to par, Hoskins said. "We had been hanging on for years," he said, "and when I got here in 1993, that legacy was hitting us right between the eyes."

The blaze not only forced the zoo's hand toward rebuilding the primate exhibit, but also galvanized public and donor support for the project. Although the real test may be carrying out the rest of the design, which will cost at least $250 million and take as long as 10 years to complete, many think the zoo's worst days are behind it.

"I would've said it was on the brink of failure after the fire," said Sydney Butler, executive director of the American Zoo and Aquarium Association, based in Silver Spring. "They've made a magnificent recovery."

The new design calls for a main street thoroughfare with paths leading to various exotic animal locales, such as a six-acre Africa exhibit, all focused on the theme of conservation and designed to allow people to get as close as possible to the animals. A decrepit 30-year-old monorail will be replaced with paddle boat rides on the lake.

Hoskins said he hopes the make-over will help the zoo to become a tourist destination. But first, the zoo needs local visitors, some of whom think the zoo deserves blame for the deaths of the primates, to rebound.

Greg and Karen Palmer, of Willow Grove, Pa., are willing to give the zoo a second chance. The couple had been members for years before the fire. They rejoined to celebrate the opening of the primate exhibit. But Greg Palmer, a retired firefighter, thinks the old zoo had an inadequate fire suppression system. The fire "should never have happened," he said.

But visiting recently with sons Jason, 9, and Nicholas, 2, Karen Palmer is heartened by the changes at the zoo since the family was last there--and not just at the primate exhibit. "There's twice the staff, everyone is well-trained, there are first-aid carts and more security," she said.

Meanwhile, a barrage of local publicity and a $1.5 million advertising blitz are fueling interest in the primates, as are the antics of these most human-like of animals.

But particularly heartwarming to Philadelphians is the homecoming of Chaka, who was born at the zoo in 1984 to John and Samantha, two gorillas who died in the fire. Demba may not be fertile, but she is valuable genetically because her parents were caught in the wild, which is no longer legal.

The couple still are getting to know one another in private. Demba has shown interest in Chaka but has screeched and screamed when he has tried to touch her, according to lead primate keeper Julie Unger Smith. Chaka has bared his teeth and gotten angry, but so far he has let her keep her distance.

Will Chaka and Demba find happiness and make babies? The gorilla soap opera will likely unfold over months, if not years, and zoo keepers are not overly optimistic, given Demba's age and lack of experience. But hopes are high at the zoo.

"After the tragedy, our responsibility was to try to find whatever positive we could out of the situation," said Andy Baker, curator of primates and small mammals. "I believe we built a facility we can be proud of, that the animals are going to enjoy, that's functional for the keepers and stimulating for visitors."

CAPTION: Tula, an orangutan, swings while Mango eyes primate keeper Chris Waldron.

CAPTION: Destruction: Snickers was one of 23 primates killed in the 1995 Christmas Eve fire.

CAPTION: Renewal: A baby lemur makes its public debut at the zoo's new primate reserve.