BigCar YouTube channel just posted a video on the Prius Story. I really enjoy his stories/videos on cars. He gives prospective on how much of a risk it is for smaller car companies like Volvo and Saab to develop a new car. I had a chance back in 1999 to test drive the right hand drive Gen1 Prius in Albany, NY. Even had a chance to meet the late David Hermance at that event.
Everybody mentions the TRW patent from the mid-20th century, but it's more rare to see a mention of how similar the Prius hybrid system is to John Godfrey Parry Thomas's patent filed in 1908. It's acknowledged in the later TRW patent, so that's one way to find it. Achievements getting built up over time. Lots of time.
I pulled up the patent linked above and started reading. Got part way through the description of the invention, than copied it and bookmarked the page.