Technically Sweet (or The Sweet) aren't traditional "Metal", but their over-the-top bombastic style with high-pitched guitars and vocals was certainly an influence on the Metal Community.

Generally they were considered more of a "Glam" band, but considering the time period songs like "Ballroom Blitz" were and  still are very heavy songs.  They used ghost-writers and had plenty of member changes that really never let the band to super-stardom, but Brian Connolly and the boys made a statement on the Rock world that will never be forgotten.