Tesla

What started with one man modifying Lotuses and other small cars with an electric powertrain, slowly turned into the largest electric vehicle (EV) producer in not only the US, but the entire world. Tesla was started by Martin Eberhard and Marc Tarpenning in 2003, with the goal of building "a car manufacturer that is also a technology company." They got funding in 2004, and were bought out by Elon Musk later that year. Now with the resources, they started modifying cars with EV powertrains, their first being a modified lotus known as the Roadster. (Note: Tesla has now re-done the roadster, now starting from scratch rather than using a lotus.) Musk eventually fully took over and started producing cars of his own, and the company grew from there.