Three is a pink number 3 with blue eyes. The youngest of the main Numbers, she rarely goes on missions due to her young age. She is often quite loud and a bit rude. She also has a collection of objects she calls "beautiful things". In later episodes, she does go out more often by herself.
She also mainly operates the Brain Gain Machine and loves ringing the doorbell to distract people. Three loves her beautiful things.
In the earlier episodes, she was accompanied by bigger numbers upon going on missions. Five usually accompanies her, though Six has also done so, once in an episode. Four also has done so but things have gone wrong upon doing so. On the first time, the Launcher broke down before Four was sent out, and on a second time, Five was unable to find a 3 for Three to land on, resulting in her landing in a cave and Seven had to rescue her and escape the cave.