Uxie is a legendary in the legendary trio, the lake gurdians, along with Mesprite and Azelf. They are meant to represent knowledge, emotion, and willpower, respectively. They are based on the Imperial Regalia of Japan: the Yata no Kagami (wisdom), Yasakani no Magatama (benevolence), and Kusanagi (valor). Parts of their names come from fantasy creatures: pixies, sprites and elves, respectively. The other parts of their names come from pronouns: you (Uxie), me (Mesprit), and us (Azelf).
Unlike previous trios, all three of the lake trio are of a single type, the Psychic-type, though like the others, they share an Ability: Levitate. According to legend, when Arceus created the universe it created Uxie, Mesprit, and Azelf, and therefore is believed to be their master. According to one of Azelf's Pokédex entries, all three of them were born from the same Egg.