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 franchise. They are always wondering off and enjoy causing mischef 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. At 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.

Like Bo, the sheep did not appear in Toy Story 3.

However, they are seen on the upcoming Toy Story 4 merchandise. This strongly indicates that the sheep will return with Bo Peep in the fourth film.