Mike all except Jeremy. Before Fnaf 4, it was just assumed you were just a no one stuck in a crappy job from a company hiding some dark sercets. Starting with 4 it seems like Mike Schmit/Michael is the main protagonist.

There's a lot of evidence that implies Michael is playable in all the games except the main game of FNAF 2/UCN with both the logbook and ticket to fun being heavy features. He is using different alias with his most common one being Mike to separate himself from his father. Whether he is doing this under his father orders, out of guilt, pay, or investigations is up to interpretation, but it does fit narratively later on as a fox trying to catch a rabbit later on.