It's debated, if you're talking about FNAF.... But I think it was Foxy.
Answer:
Although it isn't canon and nobody still knows to this day Foxy would be a higher chance of being a candidate.
1. In Fnaf 1 his jawbone is broken hence causing the mouth to be wide open. Some of his teeth are also missing
2. In Fnaf 4 if you look closely you can see on nightmare foxy's right eye there is a hidden 87 which fans speculate reference to the Bite of 87 possibly a vision he's seeing.
Explanation:
