The Prius was a big step forward for the future of green cars. Up next for Toyota and its rivals: Far more powerful batteries for next-generation hybrids, plug-in electric cars and eventually zero-emission fuel-cell vehicles powered by hydrogen, which combines with oxygen in the air to form water.

Introduced in Japan in December 1997, and the following year in the U.S., the Prius, now in its second generation, gets about 46 miles per gallon switching between a gas engine and electric motor. It has been by far the most successful hybrid, selling a cumulative 829,000 vehicles — making up for most of Toyota’s nearly 1.2 million hybrid sales. Toyota has gotten a kick from the Prius, an enhanced global image for technological innovation, social responsibility and fashionable glamour, analysts say.

The Prius is also one solid bright spot for Toyota, whose reputation for quality is starting to tarnish as it targets a record of selling 10.4 million vehicles globally in 2009. Meanwhile, its recalls are also ballooning.