The robot that WALL-E falls in love with is EVE. She is a sleek probe sent from the starship Axiom to investigate Earth for evidence that plant life has returned.
EVE's name is an acronym for Extraterrestrial Vegetation Evaluator, reflecting her mission rather than her romantic role. When she arrives on the abandoned planet, WALL-E is fascinated because he has spent centuries alone compacting humanity's accumulated trash. He follows her after she discovers the plant that may prove Earth can support life again.
Several other robots can cause confusion. AUTO is the Axiom's autopilot, GO-4 is a security robot, and M-O is a cleaning robot obsessed with removing contaminants from WALL-E. None of them is WALL-E's love interest. The 2008 Pixar film uses very little spoken dialogue in its early scenes, relying heavily on movement, sound design, and visual storytelling to develop the relationship.