Quoted By:
Okay. Charlie83 or Charlie87 or Charlie85?
In FNAF 6, Henry says (in the Insanity Ending)
"A wound first inflicted on me. I wound that I let bleed out" or something like that, referencing William killing one of his Children before the others.
What does this entail? Henry's child was the first. We can rule out Sammy because he probably doesn't even exist in the games (counterpoint: SAVE HIM minigame, a possible candidate for a retcon tho). So that's charlie, who died before the first set of murders, who are probably the MCI, which probably happened in 1985 (as hinted by altered agony memories in the ball pit from Into The Pit (Fazbear Frights vol. 1)). So we can with a certain certainty say that's Charlie83 (or even Charlie82) is true.