That's a really odd chain of music leading to Metallica, but Culture Club is an amazing start...
The first extreme metal album I ever heard was Deicide "Once Upon The Cross". My uncle gave it to be along with a mix CD with Cradle of Filth, Rotting Christ, Hypocrisy, and a Theatre of Tragedy. The Deicide kind of scared me at the time. I was 10 or 11, and I'd never heard Satanic growly shit. I really got into Hypocrisy and Cradle of Filth though. Within a year from there I was rocking out to Deicide, Morbid Angel, Hypocrisy and Darkthrone every chance I had. Man, good times.