You when you think about. Michael was the only artist to release a classic album in three different musical genres. (4 if you count Jackson 5 music).
Off the Wall was clearly a disco album.
Thriller and Bad were Pop albums that gave him the kind of Pop label.
Dangerous was literally a 90s rock album, go back and listen if you don't believe.
That's Disco, Pop, Rock. His last album Invincible was an R&B album too, althought calling it a classic might be debatable but i liked it.
And then of course his Jackson 5 stuff was 70s funk and soul music.
So technically you could even give him classics in 5 genres.