Heavy rockers Metallica will appear in an episode of the hit US TV show The Simpsons in September (06). THE UNFORGIVEN hitmakers will be special guests in the first episode of the cartoon's 18th season, and recorded their voiceovers last autumn (05). Metallica follow fellow rockers THE Rolling Stones, U2, Aerosmith and George Harrison who have all become animated guest stars on the show. Bandmates James Hetfield and Kirk Hammett have also voiced characters for upcoming Cartoon Network series METALOCALYPSE, which follows the exploits of a Norwegian heavy metal band called DETHKLOK.