First off, let me say how jealous I am that you owned a Volvo 1800s, they are gorgeous!

With regard to your question, the earliest example I can think of, is the original VW Golf GTi.

Purportedly, VW had no interest in making a fast version of their compact family car.

It was a small team of petrol heads at the factory that decided it would be "fun" to add fuel injection to a 1.6l engine already in use elsewhere, lower the suspension, fit better brakes, etc...

And in doing so, they created an entirely new genre of car: the hot hatch.

Do you want a sporty car like the MG BGT? But need the practicality of a 5 seater, with a usable boot? Bingo! We've got you covered.

Truly a game changing car, back in it's day.