You play as Michael in literally every game.
In FNAF 1 - Mike Schmidt is Michael Afton. In SL monologue, he says "They thought I was you." He's talking about the FNAF 1 animatronics.
in FNAF 2 - Fritz Smith is fired for an odor, just like Mike Schmidt. That's because Michael has a rotting odor due to being dead. He's not Jeremy Fitzgerald, just Fritz Smith.
in FNAF 3 - Who would go to a crappy horror attraction just to save some dead kids? Michael.
not in FNAF 4.
in FNAF SL, obviously.
in FNAF6 - The bear mask and the fact that Henry says "This was not intended for you", meaning that he wasn't purposefully trying to get Michael to join. He built an escape because he expected someone else, but Michael was at peace now. He dies in the fire.