The Design of Toy Story’s Rex was Done by the Director of The Avengers.
In his spare time, Joss Whedon worked on a variety of projects, including superhero films such as The Avengers and DC’s Justice League. While he was working on Toy Story, the Buffy the Vampire Slayer writers and producers got the opportunity to cooperate with him.
Even Whedon himself was involved in the development of one of the film’s most recognisable characters. The fact that the same person who directed Age of Ultron came up with Rex is astounding, to say the least.