Rosalina is a woman who is the guardian of space and the adoptive mother of the Lumas. Rosalina made her debut in Super Mario Galaxy. She lives in space with her adopted children, the Lumas, and travels the universe on the Comet Observatory. Rosalina has great power, whose sole duty is to watch over and guard the universe, the Mushroom World and protect the Lumas. Rosalina's backstory is described in her story book, which is found in the Comet Observatory's Library in Super Mario Galaxy, telling her past of her time living on Earth and how she met the Lumas. 

Voice Reference: https://youtu.be/BLzE9Z25LfM?t=3