Complex sentence: Rimensberger was the promoter of the first Metalhammer Lorelei Festival with leading metal acts such as Metallica, Motörhead, Venom etc. and originally recommended Metallica to Peter Mensch (AC/DC) for management.
Split into simpler sentences: Rimensberger was the promoter of the first Metalhammer Lorelei Festival, with leading metal acts such as Metallica, Motörhead and Venom. It was him who recommended Metallica to Peter Mensch (AC/DC) for management.