Freddy Fazbear (originally known as Freddybear, as seen in the Kickstarter) is the main antagonist of Five Nights at Freddy's. He is an animatronic bear who, like the other animatronics in the game, is left in a "free-roaming mode" at night, during which he wanders around Freddy Fazbear's Pizza, along with the other animatronics, until 6 AM, to prevent their servos from locking up.

Like the other animatronics, Freddy Fazbear will attempt to forcefully stuff any human he sees after hours into a Freddy Fazbear suit, resulting in death.

Freddy is a brown animatronic bear with a light shade of brown on both his stomach and puffy muzzle. On stage, he wears a black top hat, black bow tie and wields a microphone with his right hand. 

 He has thick black eyebrows, three-toed feet, and three blackish freckles on both sides of his muzzle. From his palms and underneath his fingers he has what appears to be paw-like prints. 

His round ears are articulated and are thus able to move backwards and forwards (Similar to the ears of several other animatronics). Freddy sports squarish, human-like teeth from his lower jaw, and, like most of the animatronics at the pizzeria (except for Foxy), has no visible teeth on his upper jaw.

He has human handprints on the right side of his face and chin from the left (see picture on the right) 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, with him and Foxy being the only two animatronics whose pupils glow in the dark.

Freddy starts the night on the Show Stage, along with his bandmates, Bonnie and Chica. Upon activation, he will follow a set path from the Show Stage to The Office. The path is as follows:

Here is the order of rooms he goes to:

Show Stage → Dining Area → Restrooms → Kitchen → East Hall → East Hall Corner → The Office.

(By the way, you might not be able to see him very well, because he always stays in the shadows.)

Unlike the other animatronics, he will remain in dark areas of the room(As I mentioned) he is occupying, leaving mostly his eyes and parts of his face visible. This implies that Freddy is avoiding the cameras as much as possible or, as Phone Guy states, this may be because Freddy is more active in the dark.

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

Freddy 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 and the player has no means of warding him off.

For the first two nights of the week, Freddy is inactive and stays onstage, looking at the camera intermittently. During those nights, he only becomes active if the player runs out of power.

After the power goes out and the player spends some seconds in the dimly-lit Office, Freddy Fazbear's face will light up in the left doorway, illuminated and shimmering, accompanied by his music box jingle. After several seconds, the remaining lights of The Office and Freddy's face will flicker and turn off, turning the room completely dark (in addition, Freddy's jingle will stop as well). 

Being initially not visible (yet sometimes audible due to his footsteps), Freddy will approach the guard and attack them, resulting in a game over.

If the player "plays dead" (i.e. does not move while he plays his jingle), his attack may be delayed. Typically, doing this may keep Freddy playing his jingle a bit longer and, when the lights completely go out, may delay his attack, giving the player a bit more time to hold out until 6 AM.