Rosalina is a character that debuted in Super Mario Galaxy, first appearing in the Gateway Galaxy. She serves as the adopted mother of the Lumas and commands the Comet Observatory. She is a princess as well as a very powerful figure, as her duty is to watch over and protect the cosmos as well as the Lumas.
Rosalina's back-story is chronicled in her storybook told by her in the Comet Observatory's Library in Super Mario Galaxy. Nine chapters are unlocked throughout the game, and the last is unlocked by completing the game.