He was an engineering wizard for Toyota with an environmentalist's heart -- an executive who championed hybrid gasoline-electric cars years before global warming entered the popular conversation.
He translated the virtues of the fuel-efficient Prius in appearances before lawmakers and scientists, promoting a car of the future that would win the embrace of a once-skeptical American public.
David Hermance, 59, of Huntington Beach, who died Saturday afternoon when his experimental plane crashed into the ocean off San Pedro, was remembered fondly for his efforts to advance the kind of technology that could one day reduce America's reliance on fossil fuels and ease pollution caused by the nation's love affair with gas guzzlers.
"He was the American father of the Prius," said Bill Reinert, his longtime colleague.
As executive engineer for advanced technology vehicles at Toyota's technical center in Gardena, Hermance played a key role in adapting Japanese technology for consumers in the United States.
The first generation of the Prius, which runs on a combination of a gasoline engine and an electric motor, received a lukewarm reception when it arrived in the United States in 2000 after its debut three years earlier in Japan.
Hermance was instrumental in helping to develop a second-generation vehicle, released in 2004, to appeal to the American public, with greater acceleration, better fuel efficiency and lower emissions.
"Dave repeatedly demonstrated his commitment not just to Toyota's profits but to the planet," said Jason Mark, vehicles director at the Union of Concerned Scientists in Berkeley. "He garnered the deepest respect from the engineering community and the policy community. His family should be tremendously proud of the contribution he made."
Hermance was Toyota's hybrid engineering ambassador to the United States. He appeared before regulators and legislators, translating the complex and sometimes arcane idiom of hybrid technology into plain English that made it seem not only plausible but appealing, environmentalists said.
"He made the Prius something that worked for the American market," said Roland Hwang, vehicles policy director for the Natural Resources Defense Council.
"When people think of hybrid systems, they think of Toyota, and that is due in good part to Dave's work. He was Mr. Hybrid, the American face of the hybrid."
Hermance spent 15 years with Toyota in a variety of engineering and supervisory roles. Before that, he was at General Motors for a quarter century, working on vehicle emissions and durability test development, according to a biography provided by Toyota. He is survived by his wife, Mary, and a son and a daughter.
Search crews Sunday morning located the wreckage of Hermance's experimental plane.
After the submerged craft was spotted using sonar, divers from the Los Angeles County Fire Department videotaped the wreckage to aid the crash investigation, said Mark Savage, a department spokesman. Savage said plans are being made to retrieve the wreckage, which was found about 70 feet below the surface.
Hermance's body was found floating in the water shortly after the crash. Hermance was the only person on board, Savage said.
The area where the crash occurred is often used by pilots for aerobatics, and witnesses said they saw the plane flying in loops and dives before the accident. Witnesses said that during one of the maneuvers the plane's engine revved and, instead of pulling out of a loop, the plane went straight into the water. One witness said that he thought he saw an unopened parachute trailing the plane.
Reinert said Hermance was an experienced pilot who loved his plane. "He was always talking about getting in it and doing" aerobatic maneuvers, Reinert said.
Authorities identified the plane as a Russian-built Interavia E-3. It had taken off from Long Beach Airport. The plane crashed about 1:20 p.m. Saturday, roughly 400 yards offshore.
The Federal Aviation Administration website classifies Hermance's plane as an experimental aircraft, meaning that it was assembled by amateurs or from a kit, or that it was a light-sport aircraft that had not received a U.S. or foreign certificate for airworthiness.
A National Transportation Safety Board report shows that an Interavia E-3 with the same registry was damaged when it ran out of fuel and made an emergency landing in a Watsonville, Calif., field in July 2000.
Times staff writer John O'Dell contributed to this report.