Toyota's Prius hybrid debuted in the Japanese market in 1997 with the internal designation NHW10, but a slightly revised NHW11 didn't reach North American shores until 2001.
This first model is the only sedan in the Prius' almost 20 year history.
The Prius was the world's first mass-manufactured compact electric car at it launch. Fuel economy, based on revised testing methods, was 42 city, 41 highway and 41 combined mpg.
The compact was motivated by the Toyota Hybrid System, which mated a 70 horsepower, 1.5-liter gasoline engine with a 44 horsepower electric motor.
The interior was spartan, by we can already see the hallmarks -- such as the eyebrow digital instruments -- that would define the Prius' dashboard design for years to come.
In 2003, the next generation Prius debuted. Sold as a 2004 model with the XW20 internal codename, the second generation model solidifies Prius design language going forward.
The Prius grows to a midsize class and transforms into a hatchback. Every Prius model that flows will have a similar hatchback profile.
The new slippery body results in an aerodynamic 0.26 coefficient of drag.
The Toyota Hybrid System II under the hood mates a 1.5-liter, 76 horsepower gasoline engine with a 67 horsepower electric motor. Total system power is stated at 110 horsepower.
The interior is more spacious than the first-gen, but retains the standard central screen and horizontal digital display at the base of the windshield. Like all Prius vehicles, there's no conventional gauge cluster ahead of the steering wheel.
Toyota's Hybrid System II stores its electric energy in a 1.31 kWh nickel metal-hydride battery pack. That capacity and technology doesn't change much for two generations and four models.
The EPA figures the Prius will do 48 mpg during city driving, 45 mpg on the highway driving and return 46 mpg combined.
In 2009, the 2010 model year Prius made its debut. Of course, it was larger, more efficient and easier to live with.
The third generation model hides major revisions beneath a body's design that doesn't change significantly.
The coefficient of drag drops to 0.25, keeping the Prius in its position as the most aerodynamic production car on the road at the time.
Toyota's Hybrid System grows to accommodate a 1.8-liter, 98 horsepower gasoline engine, which brings total system horsepower to 134 ponies.
The interior design continues to evolve, becoming more futuristic in this third generation.
The electronic shifter gains a jewel-like translucent blue hue.
The eyebrow display at the top of the dashboard grows to accommodate and display more data.
Despite being more powerful and larger, the Prius continues to grow more efficient.
EPA estimates grow to 51 mpg city, 48 mpg highway and 50 mpg combined.
Model number XW40 belongs to the slightly larger offshoot of the Prius family, the Prius v. The more "versatile" variant features more space for those who need it.
Next, Toyota adds the compact, city-friendly Prius c to the mix. The smaller model is a bit more efficient in the city than the third-generation Prius, but a bit less on the highway.
The fourth generation Prius arrived just this year with the internal designation XW50. The new model features a radically styled design. However, if you look closely, you'll see many of the hallmarks of Prius design.
Like the previous two generations, the new Prius is an elongated liftback.
Active and passive aerodynamic tricks help Toyota to further streamline the hybrid, reducing the coefficient of drag to just 0.24.
The Hybrid System actually steps down in power. Peak system power is stated at 121 horsepower, but the transmission has been tweaked to use that power more efficiently.
Inside, the cabin makes a major step up in maturity and fit and finish, but does so while keeping the elements that make a Prius a Prius.
The electronic shifter retains its asymmetrical design and translucent blue material, but now features a tulip shape that is simply gorgeous.
The eyebrow cluster at the top of the dashboard is now a full color array of displays that is as easy to interact with as ever, despite boasting more information than ever.
Fuel economy jumps to 54 mpg in the city, 50 mpg on the highway and 52 mpg combined thanks to improved aerodynamics and a lighter lithium-ion battery pack.
The split rear glass and vertical taillights are other hallmarks of Prius design that can be traced back to that second generation model.
The details are a bit extreme, which causes many onlookers to recoil, but the broad strokes, silhouettes and themes still fall in line with the previous two generation models.
And the future of Prius design looks even more extreme. The upcoming Prius Prime plug-in hybrid will evolve the design of the fourth-generation model when it hits the road later this year.