Harry Wegeforth was the San Diego Zoo's founding force — a man of enormous energy and firm opinions who directed the institution through its formative decades. He acquired animals aggressively, sent collectors abroad, and ran the zoo with the intensity of someone who understood that he was building something that would outlast him.

But the most interesting executive the zoo produced in its early years was Belle Benchley, whom Wegeforth appointed to manage the institution's operations in the 1920s. She had been the zoo's bookkeeper, hired in 1925; Wegeforth gave her increasing responsibility until she was effectively the director, and eventually gave her the title to match. From 1927 to 1953, she ran the San Diego Zoo — the only female zoo director in the world for most of that period, managing a major public institution at a time when such positions were almost uniformly held by men.

Among the many animals who have lived at the San Diego Zoo over its century of operation, Ken Allen achieved the most distinctive celebrity. He was a Bornean orangutan known throughout San Diego as 'the hairy Houdini' for his repeated escapes from his enclosure in the 1980s.

Ken Allen's escape methodology was creative and persistent. He tried different approaches, observed what worked, and adjusted. Zoo staff installed successively more elaborate barriers; Ken Allen found the gaps. The city followed his exploits with the enthusiasm usually reserved for sports teams. When he died in 2000, the San Diego Union-Tribune ran his obituary on the front page. He demonstrated, as animals sometimes do, that the intelligence of the creatures in a zoo's care has a way of exceeding the intelligence of the infrastructure designed to contain them.

The San Diego Zoo's transition from entertainment to conservation institution represents one of the more significant changes in American public science during the twentieth century. The zoo's Institute for Conservation Research conducts breeding programs for endangered species that have produced results measurable in the recovery of populations that might otherwise have vanished.

The zoo's giant panda program was among the most successful in the world during the years that pandas were in residence. Bai Yun and her various mates produced six cubs at the zoo between 1999 and 2012, including Hua Mei — the first giant panda cub born in the United States to survive to adulthood. The breeding successes established San Diego's scientific credibility in species preservation, an area that has become central to the zoo's identity and mission.

The San Diego Zoo occupies 100 acres in the northern section of Balboa Park, and its presence shapes the park's character as much as any of the museums or gardens that share the space. The Skyfari gondola — built in 1969 by a Swiss tramway company — gives visitors an aerial view of the collection, a perspective that reveals the zoo's ambition: habitat areas designed to approximate the environments of the animals they hold, arranged across a canyon landscape that Balboa Park's topography provides naturally.

More than a century after Harry Wegeforth looked at a cage of homeless exposition animals and decided to build a zoo, the institution he founded remains one of the most visited in the world. The animals have changed, the enclosures have changed, the mission has changed from entertainment to conservation. What has not changed is the fundamental transaction: people looking at animals, animals providing the occasion for people to think about the natural world they share with everything else alive.