There is no way to convey to you how unbelievably cool Michael was in the 80's and how amazing his fresh new sound was. The sidewalk lighting up as he walked on it in the Billy Jean music video was the coolest thing we'd seen on TV back then. He perfectly blended music, dancing, fashion, style, attitude, and theatrics to create an entire persona that all the listeners and viewers could share in. He set trends, broke records, and topped charts. I cannot convey what it felt like to back then to young people because there hasn't been anything that original since the 90's when Nirvana and Grunge exploded across the music scene. I wish there was something recent to point to and say "it was like that!", but there's nothing.
It's very similar to the previous "King". Elvis Presley was not just a good musician, he was a cultural statement.
When people first heard him sing on the radio they were sure they were listening to a black singer, but when he started talking in interviews it became very obvious that that he was not.
Michael Jackson did something similar. He came from the musical background of black Soul bands, but as a solo artist he covered a variety of styles that were unexpected from a black musician. It's not a coincidence that a lot of his songs deal with social issues as well ("It doesn't matter if you're black or white.", "Heal the world.", "start with the man in the mirror" where most songs of other artists are about love or having a party).
I didn't care much about Michael Jackson when I was growing up in the 80s and 90s, but I came to appreciate his talent more once I was older. Aside from some of the other things that were already mentioned, he was known for some insanely unique and distinctive dance moves, and everyone wanted to do them. You know how kids these days are 'dabbing' or doing these dances that they saw on fortnight or wherever? Where did any of those popular moves originate from? I have no idea. But when you saw someone doing a Michael Jackson move, you knew EXACTLY who it came from.
Go back to the 70's and 80', witness the insane popularity of songs by the Jacksons, and in particular how popular Michael's songs were.
He also did duets with other artists and I believe he had hand in songs that became popular with other artists.
That's all, really. The Jackson's had their finger on the pulse of pop. And I say this as someone who never listened to their music intentionally, even I was very aware of it (and will admit much of it had a strong appeal).
Edit: Pop is tricky to stay on top of. By definition, "popular" music has the broadest appeal, which also means it's less complex. The more complex music is, the smaller the group that can appreciate it. I like to use Miles Davis' "Kind of Blue" as an example - I have musical training and still find it challenging to "grok".
So Michael and family had an unusual ability to change going forward, and keep their music engaging, while still having a broad appeal. Few musicians can do this, let alone to Michael's level.
I like to use Miles Davis' "Kind of Blue" as an example - I have musical training and still find it challenging to "grok"
Say what? Kind of Blue is very popular for the genre. I'm middle-aged, but I don't know anyone who doesn't appreciate that album. It sold more than 5 million albums in the US alone, making it a landmark jazz album.
Not "the same", more like "same enough" to have broad appeal - that is he understood what was immediately accessible in music, but it wasn't always the same thing. That's what was so brilliant about his music.
Good marketing and lucky timing. He benefited greatly from the rise of MTV and music videos. With his talents for music and dance, he was the right person at the right time to really take off. His music videos were good.
And his PR people did fantastic work marketing him. Whoever convinced Disney to make the Captain EO ride at Disneyland was a genius.