Arquillian

Arquillians are a small sapient alien species from the planet Arquillia.

Overview
Arquillians are a small species. They wear a Human-sized mechanical suit, which is used for both protection and locomotion (also hiding their true form). Much of their energy goes to "drive" the mechanical human-suit, but they have a "autopilot" mode for making their life easier. To get the human suit to work, they have to download software programs to the brain. Too much information and the computer will have a meltdown, resulting in them divulging their true identity. They also possess a powerful weapon.

In the movie the MiB need to find the galaxy and return it to the Arquillians, who are threatening to annihilate Earth if it is not returned within a certain time period.