Luxo Jr. - Pixar

"Pixar Animation Studios has long believed in making short films. In 1986, Pixar's first-ever short, Luxo Jr., launched a new direction in animated filmmaking, using three-dimensional computer animation to tell a story." - Pixar official website.

The Adventures of André and Wally B. was created at the Lucasfilm Computer Graphics Project, which later spun off Pixar Animation Studios, so it is technically not a Pixar short.