The Japanese carmaker that introduced the world's first mass-produced hybrid car was Toyota.
Toyota launched the Prius in Japan in December 1997 after developing it as a fuel-efficient “car for the 21st century.” The first-generation Prius combined a gasoline engine with an electric motor and battery, allowing the powertrain to use electric assistance, regenerative braking, and engine operation more efficiently than a conventional car.
Toyota's achievement was mass production and market introduction, not the invention of every hybrid concept. Earlier experimental, prototype, and limited-production hybrid vehicles had existed. The Prius was the breakthrough that brought gasoline-electric hybrid technology to ordinary consumers at meaningful scale.
The Prius initially sold only in Japan. Toyota expanded it to other markets beginning in 2000, while Honda's two-seat Insight followed as another important early modern hybrid. That timing is why “first mass-produced hybrid” is more precise than simply calling the Prius the first hybrid vehicle ever built.