Heartland rock... Petty's early success in the UK helped trigger his American popularity, after his first album was released to little fanfare in the States. Always a unique mix of greaser/rocker (but not "southern" rock especially), he was all modded out for his first few appearances on the Old Grey Whistle Test.
The 1977 single American Girl off his debut album did little at first, but has since entered the Petty canon and American radio soundscape. Heard it this morning in the donut shop. Good stuff.