A lot of people think that Golf GTI (Mk I) is the first hot hatch. It's not true. The first hot hatch was the Renault 5 Gordini.
And, the even more exciting thing is, that, the 'Sport Golf', as the engineers called it, was an 'evening and weekends' project, developed in secret outside normal working hours, because Marketing and Management just didn't see that there was a market for it. Boy, were they wrong! :)