WALL-E went undeveloped during the 1990s partly because Stanton and Pixar were not confident enough yet to have a feature length film with a main character that behaved like Luxo Jr. or R2-D2.^[8] Stanton explained there are two types of robots in cinema: "human[s] with metal skin", like the Tin Man, or "machine[s] with function" like Luxo and R2. He found the latter idea "powerful" because it allowed the audience to project personalities onto the characters, as they do with babies and pets: "You're compelled ... you almost can't stop yourself from finishing the sentence 'Oh, I think it likes me! I think it's hungry! I think it wants to go for a walk!'"^[35] He added, "We wanted the audience to believe they were witnessing a machine that has come to life."^[6] The animators visited recycling stations to study machinery, and also met robot designers, visited NASA's Jet Propulsion Laboratory to study robots, watched a recording of a Mars rover,^[15] and borrowed a bomb detecting robot from the San Francisco Police Department. Simplicity was preferred in their performances as giving them too many movements would make them feel human.^[6]

Stanton wanted WALL-E to be a box and EVE to be like an egg.^[36] WALL-E's eyes were inspired by a pair of binoculars Stanton was given when watching the Oakland Athletics play against the Boston Red Sox. He "missed the entire inning" because he was distracted by them.^[37] The director was reminded of Buster Keaton and decided the robot would not need a nose or mouth.^[38] Stanton added a zoom lens to make WALL-E more sympathetic.^[38] Ralph Eggleston noted this feature gave the animators more to work with and gave the robot a child-like quality.^[30] Pixar's studies of trash compactors during their visits to recycling stations inspired his body.^[6] His tank treads were inspired by a wheelchair someone had developed that used treads instead of wheels.^[36] The animators wanted him to have elbows, but realized this was unrealistic because he is only designed to pull garbage into his body.^[6] His arms also looked very flimsy when they did a test of him waving.^[36] Animation director Angus MacLane suggested they attach his arms to a track on the sides of his body to move them around, based on the inkjet printers his father designed. This arm design contributed to creating the character's posture, so if they wanted him to be nervous, they would lower them.^[39] Stanton was unaware of the similarities between WALL-E and Johnny 5 from Short Circuit until others pointed it out to him.^[8]

Auto, the captain and EVE