Ben Fong-Torres sums it up. You should read the entire, brief article, but here is the key:
Which helps answer the second question: With the J5 and the Jacksons (their name after they left Motown in 1975 and had their first personnel changes), and as a solo artist, Jackson shattered the categories that have always been part of popular music.
The J5 were the first crossover act, attracting fans of all ages, getting airplay on both Top 40 and FM “progressive rock” stations, and selling to blacks, whites – all colors. With the Motown machine behind them, they pumped out music that might be labeled “bubblegum,” but blended solid R&B, funk and rock, executed perfectly by the guys and fronted by a cute, miniature version of James Brown and Jackie Wilson.
As they grew, the spotlight stayed on Michael, who remained loyal to his brothers but scored big hits on his own – never more than with “Thriller,” whose sales have reportedly hit 100 million units since its release in 1982. With his “moonwalk” on Motown’s 25th anniversary special, he galvanized a nation.
Suddenly, he was a dancer in a league with Astaire and Kelly; he was a mainstream show-business superstar – the biggest force in pop music. Once again, colors and categories meant nothing.
I saw Fred Astaire talking about MJ once, and he was saying MJ was about the best dancer/entertainer he’d ever seen:
“Oh, God! That boy moves in a very exceptional way. That’s the greatest dancer of the century.” – Fred Astaire
“I didn’t want to leave this world without knowing who my descendant was. Thank you Michael!”- Fred Astaire (shortly before his death)
Even Frank Sinatra held him in high regard as a singer:
“The only male singer who I’ve seen besides myself and who’s better than me – that is Michael Jackson.” – Frank Sinatra
Frankly, I have always felt sad about the way Michael’s life turned out. He was a tremendously talented entertainer who had a very difficult life off the stage. He never had a chance at a “normal” life. He was thrust into the limelight at an extremely early age, and pressured to maintain schedules that would knock any adult off their feet. His self-image was terrible, thanks in large part to his father’s near total rejection, and that’s just the tip of the iceberg. I always wished he would continue performing, because he was so amazing to watch and listen to, but he just couldn’t deal with it all, and that’s just sad. Our culture chews up celebrities and spits them out, often with nothing but scorn in return for the privilege. He didn’t start out being twisted, fame did that to him.