In the 1950s and '60s, golden boy crooner Pat Boone built a career around recreating lily white versions of classic rock and roll numbers for American consumers who were too sensitive to cope with Elvis Presley's gyrating pelvis, Jerry Lee Lewis' pumping piano, or, God forbid, African American performers like Chuck Berry and Little Richard.

Thankfully, by the 1970s the civil rights movement had changed a few things, including the need for segregating popular music, and so Boone refocused his career on religious music - something he would remain focused on until 1997, when, for reasons still somewhat beyond belief, he inexplicably found himself ... 'In a Metal Mood.'

Maybe this had something to do with the fact that heavy metal was about as unfashionable at the time as it had ever been (the watered-down American hair metal variety, anyway; overseas, extreme creativity still flourished): exiled to the fringes of music consumers' conscience by grunge's slate-cleaning drudgery, and thus just about unfashionable enough to capture Pat Boone's attention.

In any case, the self-explanatory 'In a Metal Mood: No More Mr. Nice Guy' reintroduced a hilariously leather-clad Boone to the Billboard charts after a 30-year absence, and showed the singer reinterpreting vintage metal classics by everyone from Judas Priest to Metallica, Led Zeppelin to AC/DC, Van Halen to Guns n' Roses, Alice Cooper to Deep Purple, and beyond, in a big band lounge/jazz format.

But the best and most press-baiting of the bunch may have been Boone's schmaltzy cover of Ozzy Osbourne's 'Crazy Train' - not least because its original singer stood for almost everything Boone did not, and caused the greatest amount of controversy amongst Pat's conservative Christian fan base.

Ozzy's version was, of course, one of heavy metal's signature songs of the 1980s, and the foundation of his solo band sound, thanks to the historic contributions of guitarist Randy Rhoads. It's no exaggeration to admit that every subsequent Ozzy Osbourne band song and album has attempted to live up to 'Crazy Train's near perfect example of powerful but catchy metallic brilliance.

And while for Boone, that particular song choice probably caused more grief than it generated record sales, Ozzy, at least, saw the entire episode as good fun, later tapping Boone's cover to act as the theme of this MTV reality show, 'The Osbournes.'

Watch Ozzy Osbourne Perform 'Crazy Train'