Sparky

Sparky is the main antagonist and titular character of Five Nights at Sparky's. He is an animatronic who, like the other animatronics in the game, is left in a "free-roaming mode" at night, during which he wanders around Sparky's Pizzaria, along with the other animatronics, until 6 AM.

He forcefully stuffs any human he encounters after-hours into a Sparky suit, as do the other animatronics, resulting in said person's death.

Appearance
Sparky is an animatronic wearing a costume that gives him the appearance of a dog. On stage, he wears a black top hat and a bowtie while wielding a microphone in his right paw. His ears are articulated and are thus able to move back and forth.

He has human handprints on his face, though they are difficult to locate. His irises are normally of a light blue color, but he is commonly seen with his endoskeleton eyes on-camera and in one of his jumpscares, rather than his normal costume eyes

Locations
Sparky starts the night on the Show Stage, along with his bandmates, Sharky and Milo. Upon activation, he will follow a set path from the Show Stage to The Office. The path is as follows: Show Stage → Dining Area → Restrooms → Kitchen → East Hall → East Hall Corner → Hallway → The Office.

Unlike the other animatronics, he will remain in dark areas of the room he is occupying, leaving mostly his eyes and parts of his face visible. This implies that Sparky is avoiding the cameras as much as possible or, as Phone Guy states, this may just be due to the fact that Sparky is more active in the dark.

Sparky will not be visible if another animatronic is in the same room as him. Viewing Sparky on the security cameras will slow him on his path, even if he is not visible in the room due to Sharky or Milo's presence.

Sparky will play his jingle either when he is in the Kitchen, where he is not visible as that room's camera is disabled, or in The Office when the power is out ( In Limited Power Night) and the player has no means of warding him off.

