Alan Rabinowitz, a zoologist who overcame a debilitating stutter to become a powerful voice for leopards, jaguars and other wild cats threatened by humans, died Aug. 5 at a hospital in Manhattan. He was 64.

The cause was cancer, according to a statement from Panthera, a wild-cat conservation organization that he co-founded in 2006 and, until recently, led as chief executive. Dr. Rabinowitz had been diagnosed with chronic lymphocytic leukemia in 2001.

As a child with a severe stutter, Dr. Rabinowitz spent much of his free time playing on the floor of his bedroom closet, where he secluded himself with “a little menagerie” of pet chameleons, snakes, turtles and hamsters — “the only living beings around me that seemed to listen but not judge.”

Dr. Rabinowitz went on to conquer his speech disorder and become “the Indiana Jones of wildlife protection,” as Time magazine once called him, braving 500-mile hikes through the wilderness, vampire bats, attacks of leeches and malaria, and a plane crash in the jungle, to preserve wild cats from Latin America to Southeast Asia.

At the Wildlife Conservation Society, where he worked for nearly three decades before moving to Panthera full time in 2008, Dr. Rabinowitz gained international renown for his research on jaguars, tigers, rhinos, bears, raccoons, leopards, leopard cats and civets.

In Belize, his work was credited with spurring the creation of the Cockscomb Basin Wildlife Sanctuary, the world’s first jaguar preserve; in Myanmar, he discovered a deer known as the leaf muntjac — “an animal so tiny that hunters wrap it in a single, albeit ample, leaf from a tropical plant,” according to the New York Times.

In recent years, he linked the world’s declining populations of big cats to the rise of infectious diseases such as SARS, West Nile virus and Ebola, saying that these apex predators “stabilize and help balance the ecological food webs to which they belong.”

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But Dr. Rabinowitz also “went beyond the science,” said biologist and conservationist George Schaller, to convince foreign governments and local populations of the importance of protecting animals, especially those that are seen as a nuisance, threat or a lucrative source of fur.

“Nobody goes to Belize, or anywhere else, and establishes a reserve — you convince the government to establish it. That takes a certain political sense,” said Schaller, who serves as vice chair of Panthera’s science council. “It takes passionate people like Alan to be on the ground in these countries, sometimes for several years, to reach the trust of the government and convince them to protect something. And that’s not what you train for as a scientist.”

Dr. Rabinowitz successfully pressed the military leaders of Myanmar, also known as Burma, to create the world’s largest tiger reserve, a sanctuary in the Hukawng Valley nearly as large as Vermont. He said his work was actually easier “in communist countries and in dictatorships than in democracies,” where he was often frustrated by slow-moving agencies and bureaucratic red tape.

“I find that most of these dictators — they’re not nice people, and I’m not an apologist for the ones I work with, but I will do anything I can to save animals,” he said in a 2008 appearance on “The Colbert Report.”

Dr. Rabinowitz also helped create the largest nature preserve in Taiwan; drew international attention to tigers in Thailand, where the United Nations added a wildlife sanctuary to its World Heritage list in 1991; and, in the Himalayan mountains of Bhutan, identified a previously unknown population of high-altitude tigers.

Still, he maintained a particular affinity toward jaguars, which he often described as “an indomitable beast” — the title of a 2014 book about his conservation efforts surrounding the animal — and which had fascinated him since childhood.

Born in Brooklyn on Dec. 31, 1953, and raised in Queens, Alan Robert Rabinowitz recalled that as a boy, he was often taken to the Bronx Zoo by his father, a physical-education teacher who served as an Army paratrooper in World War II.

“I would always be drawn to this one cage, with a solitary jaguar,” he told National Geographic in 2014. “All the other cats would charge at the bars or vocalize. But the jaguar would mostly stay quiet, watching everybody pass by, in a world of its own. That’s the way I felt. So I would go to the bars, wait until nobody was around, and talk to the jaguar — tell it my hopes and dreams, whether it was a bad day at school or how stupid I felt people were because they didn’t try to understand me.

“And I would never leave that enclosure without promising the cats that if I ever found my voice, I would try to be their voice and help them,” he continued. “I had no idea what I would be in life or that I would ever work on jaguars. All I knew is that these cats made me feel whole. They were like me, trapped inside a cage not of their making.”

Dr. Rabinowitz overcame his stutter while studying biology and chemistry at Western Maryland College (now McDaniel College) in Westminster, Md., where he graduated in 1974. At the University of Tennessee, he received a master’s degree in ecology in 1978 and a doctorate in ecology in 1981, focusing on the endangered gray bat before shifting his research to raccoons in Great Smoky Mountains National Park.

It was Schaller, who met Dr. Rabinowitz while visiting Tennessee, who suggested he begin studying jaguars in Belize. He soon received a fellowship from the Wildlife Conservation Society — then the New York Zoological Society — and came on as a researcher, with an office not far from the jaguar cage at the Bronx Zoo.

Dr. Rabinowitz wrote more than 100 scientific articles and several books for a popular audience, including “Jaguar: Struggle and Triumph in the Jungles of Belize” (1986) — published the same year he succeeded in establishing the jaguar preserve in that country — and “A Boy and a Jaguar” (2014), an autobiographical children’s book.

He was also featured in television programs including “60 Minutes” and in the 2015 documentary “Tiger Tiger,” which followed his travels to the Sundarbans, the vast mangrove forest on the border of India and Bangladesh. By then, he had been diagnosed with leukemia and had two children with his wife, the former Salisa Sathapanawath, a geneticist. (They were married at the home of actress Jane Alexander, whom he met while working in Belize; she now serves on Panthera’s advisory board.)

“I have two choices in my life now,” Dr. Rabinowitz said in the film. “I can play it very, very safe and sit at home, and maybe prolong my life by a few years and be there for my kids . . . Or I can be the person who I am, and who makes me feel best, and be the father I want them to know — but maybe cut my life short with them.”

“I’m really good at what I do, and the best thing I can do is be a model for them,” he said, explaining his reasons for leaving to make the expedition. “Not a bad father, but not an ever-present father.”

In addition to his wife, survivors include his children, Alexander Rabinowitz and Alana Rabinowitz, all of Mahopac, N.Y.; and two sisters.

At Panthera, which he formed with billionaire investor Thomas S. Kaplan, Dr. Rabinowitz oversaw projects including the Jaguar Corridor Initiative, which aims to protect jaguars across the full range of their native habitat, from Mexico to northern Argentina.

Last year, he began the Journey of the Jaguar, an expedition in which he planned to traverse the length of that habitat over four years, in chunks. After leading his team through the Mexican state of Sinaloa, despite security concerns from Mexican friends and colleagues, he was diagnosed with appendicitis and then pneumonia.

Dr. Rabinowitz was still “in recovery and out of shape,” said Howard Quigley, executive director of the Panthera jaguar program, when he rejoined his team to continue the trip in Honduras, Colombia and Brazil, ultimately covering about 4,000 miles of jaguar habitat.

“The Jaguar Journey will continue,” Quigley wrote in an email, with trips to Brazil, Mexico and the Colombian Amazon. “All of them will be to commemorate his legacy, the legacy of Mr. Jaguar, or Papa Jaguar, as the Latinos in our program call him.”