Pleasantly surprised to see sensible suggestions here today! I broadly agree with most of the consensus here: you need Sabbath here, some kind of NWOBHM rep (Maiden or Priest), probably Metallica, plus something representing more extreme styles (Slayer or Death cover this pretty well). I'll throw a wildcard into this last slot, which I think manages to cover extreme metal (in more ways than one), "hipster" metal, and popular notoriety well.
Black Sabbath - Paranoid
Iron Maiden - The Number of the Beast
Metallica - Master of Puppets
Burzum - Filosofem
Would be great to do this for other genres!
And if you don't know, now you know.