Miles Morales was introduced in 2011 in Ultimate Fallout #4. The first issue of his own title followed pretty quickly and he's had a solo title of one form or another ever since. He was a big player in the Spider-Verse and most recent Secret Wars crossovers. He has been featured in team books including Ultimates, Avengers and Champions titles. He was basically the only element of the Ultimate Comics universe deemed worth keeping after Secret Wars and grandfathered whole cloth into the MCU proper. He has also made a smattering of appearances in Marvel animated series before now. He is without a doubt one of the most pushed Marvel characters of the last decade.
So anyone claiming to be a Spider-Man fan and whining about how “Spider-Man isn't black” in the comment sections under that Into The Spider-Verse teaser trailer can sod right off. I feel quite confident in proclaiming it is impossible to have read Spider-Man comics from the last half-decade without being aware of this character.
So the big question: Fake of Dishonest Geek Boys?
The truth is that however we answer that question its just gatekeeping bullshit. This character exists, is something of a big deal and your precious white boy Peter Parker is absolutely fine. Hell, the trailer even goes out of its way to say Miles isn't the only (read: “proper”) Spider-Man which pisses me off slightly.
(Okay, I exaggerated a little in that last paragraph:, Peter Parker has never been “fine”, that's sort of the point of the character. But you know what I mean).
Let us also tackle another issue that always comes up in these sorts of discussions: why Miles is the black Spider-Man instead of the black character with his own superhero identity. That's an easy one: economics. The comicbook industry is in a terrible state because stupidity and cannot afford to create wholly original characters, hence the recent proliferation of legacy identities. Not that there isn't something to be said for giving a big name identity like Spider-Man to a character purely for representation purposes (hell, I remember what a big thing it was for some of the black boys at my school when the Red Ranger identity passed to a black character) but it is mainly the economics of wanting people to actually give the new character a chance.
Rant over. As you were.