Billy, Goat, and Gruff

Billy, Goat and Gruff are three porcelain sheep joined together and sometimes mistakenly believed to be a single sheep with three heads who are minor characters in the Toy Story series. They are always wondering off and enjoy causing mischief and when they do, they can only be stopped by their shepherdess, Bo Peep.

Toy Story
In the first film when Andy has set a stage portraying Mr. Potato Head as One-Eyed Bart, he threatens to have the sheep run over if Bo Peep doesn't keep quiet as he 'robs' the bank. Later when Woody gathers the toys for a staff meeting, Bo Peep pulls Woody over and thanks him for saving her sheep then asks if he'd like her to get someone else to watch them that night, (meaning she wants the two of them to go on a date.) Later in the film, Bo is stroking their heads when Hamm tells the toys that he sees Woody next door. In the end, the sheep are seen above Woody and Bo Peep with a branch of mistletoe.

Toy Story 2
The sheep are first seen returning with Bo from searching Molly's room for Woody's hat. Bo goes to calm Woody down and is about to kiss him but is interrupted by her sheep who are playing tug-of-war on a video game controller with Rex, prompting her to whistle to attract their attention.

Toy Story 3
Like Bo Peep and the other toys in Andy's room, the sheep were given away. Unlike their shepherdess, however, they didn't appear in any home footage at the beginning of the film. Their disappearance along with Bo, as well as their time spent away from Woody and the gang will be explained in the upcoming short "Lamp Life".

Toy Story 4
In Toy Story 4, the sheep returned with Bo Peep and play a major role in the progression of the film. As shown in a sneak peek, their names are revealed (from left to right) as Billy, Goat, and Gruff, a reference to the Norwegian fairy tale. Woody is surprised to learn their names, expressing how Bo Peep never told him, but she counters that Woody never asked. When Bo tries to persuade Woody to come with her when she and her sheep are being given away, the sheep make room for Woody in the box, (which shows that even they want him to join them.) But Woody decides to stay with Andy.

Along with Bo Peep they left the antiques store they were sold to to live a life of adventure. They are now covered in stickers. The sheep help Bo collect random objects to use for repairs in case they or any of the lost toys they are helping get damaged. When Woody is reunited with Bo at the carnival, the sheep are thrilled to see him. They tackle Woody to the ground and begin licking his face (indicating that they have missed him very much.) The sheep take part in the drama with The Bensons in retrieving Forky from Gabby Gabby. When Woody is about to head home, he tells the sheep to take care of Bo, but eventually Woody decides to stay with them.

Trivia

 * Their names are a reference to The Three Billy Goats Gruff.
 * In the 4th movie they have gone through a design change and have shorter noses and appear slicker.