Chuck E. Cheese is one of the animatronics at Chuck E. Cheese, and got shipped into Freddy's as a guest star, but they didn't expect Chuck to also move at night...
Looks the same as the Chuck E. animatronic from CEC.
On Night 3, Chuck starts moving from the Show Stage to the kitchen, then he starts playing a slowed down version of "Cheese is Funner".
An hour later, he will move to the west hall, then whisper unsettling things, then moves to the west hall corner. If he gets to the left door, he will make the power go out, and will play "Havin' a Party!" while flashing in the left door. He only kills you if he catches you moving while playing his music. If you stay completely still, the power will turn back on.