Rex

Rex is a plastic Tyrannosaurus-Rex with a lot of anxiety from an inferiority complex ("I don't think I could take that kind of rejection!") .He is insecure about his lack of ferociousness. He is voiced by Wallace Shawn. Rex's worst fear (after Sid) is that Andy will gain another, scarier dinosaur. By the end of the first film, he seems to have gained confidence throughout the movies expressing hope that Andy will receive a leaf-eating dinosaur for Christmas that Rex can play with and intimidate.

Toy Story
In Toy Story, he states that he was made by a subsidiary of Mattel (Coincidentally, real-life Rex toys are now made by Hasbro.).

Rex tries to avoid confronting Woody when he is accused of trying to jealously kill Buzz Lightyear, but slowly and reluctantly turns against him under peer pressure, quickly experiencing guilt later on. He is known to have a queasy stomach and actually barfed when he saw Buzz's dismembered arm.

Toy Story 2
It is revealed in the sequel that he is a video game fan and is very frustrated that he cannot beat the "Buzz Lightyear: Attack on Zurg" video game. He goes on a mission led by Buzz to rescue Woody after Woody is stolen by Al McWhiggin of Al's Toy Barn. After the toys enter Al's Toy Barn, Rex excitedly finds a "Buzz Lightyear" video game manual, only to lose it later, but is still able to give Buzz (the toys take an "alternate" Buzz instead) some secrets he has acquired from the manual. Rex is considered to be the heaviest of Andy's toys when he loses his grip on the new Buzz's utility line and pushes the toys to the bottom, causing the new Buzz's strength to give out. Later, "alternate" Buzz and the toys use Rex as a battering ram to break into Al's apartment. After the toys leave the apartment, they encounter a Zurg action figure, whom "alternate" Buzz duels with Rex watching. As Zurg is about to finish the "alternate" Buzz off, Rex accidentally knocks Zurg off the elevator with his tail, and finally overcomes his frustration of not being able to defeat Zurg previously.

Trivia

 * In Toy Story on Ice, Rex has a wife named Mrs. Rex.
 * Rex quotes a few of George McFly's lines from Back to the Future: "I don't like confrontations" and "I don't think I could take that kind of rejection."
 * Rex makes a cameo in the outtakes for Monsters, Inc. where he tries out for the role of Ted, the gigantic monster who Mike and Sulley say hi to on the way to work.
 * You can hear Rex's voice from Wallace Shawn in The Incredibles as Mr. Huph.
 * Rex appears at the beginning of WALL•E for a brief second when WALL•E is opening the door of his truck, but since it's a close-up it can be very easy to spot.
 * While inside Al's Toy Barn, Rex jumps out of the car once, and while chasing the car to catch up, Mr. Potato Head views him in a rearview mirror. This is a parody of a scene in Jurassic Park when T-rex appears in a rearview mirror when chasing a crew in a jeep.
 * Rex was made in 1989.