Alastair

Alastair is a Fazbear Entertainment (Inc.) animatronic. He is an axolotl animatronic initially made for parties and entertainment. He is designed to play music with speakers in his gills (the appendages that come out of axolotl heads). 

He is possessed by XXXX, a child (10) who, back in the day, William Afton had attempted to kill in the rural location of Fazbear Dine-in Fun! during his experimental days of murdering children to get them to possess animatronics. He was the first animatronic William killed for Fazbear Drive-thru Fun!

XXXX was declared a missing child as there is a camping site near the road where Fazbear Drive-Thru Fun! is, as well as it being rural. He was never found (duh) and remains an unsolved missing child case.

Maizie doesn't see Alastair move around the hallways until Night 3, which is when she is forced to go through the vents because the combined activity of Alastair and Payton is too much and Maizie can't hide from both of them until Night 5 when she can fight them. 

Before that, Alastair is usually in the office rooms, which Maizie has to use the camcorder to take photos to see where Alastair is. If she uses the flash, then he is disabled for a few moments as his vision is blinded.

DIALOGUE:

"If you continue, you'll be all alone,"

"Don't roam here alone,"

"Don't worry, I'm here, you're not alone,"

"Don't run away,"

"Do you want to listen to my m-mu-m-musi-si *glitches* s-screams?"