Rosalina is a character introduced in the Super Mario universe in Super Mario Galaxy. She is a self-proclaimed "watcher of the stars," and lives in a massive observatory in outer space named the Comet Observatory. She lives among little star creatures called Lumas, whom affectionately refer to her as "Mama." In Japan, her name roughly translates to "Rosetta". She is voiced by Mercedes Rose.
Super Mario Galaxy
In the original Super Mario Galaxy, Rosalina offers Mario and Luigi aid in rescuing Peach from Bowser in return for their help in gathering all 242 Power and Grand Stars to restore power to the observatory. She also appears at the end of the credits and tells the player thanks for all the hard work if 120 stars have been collected.
It is also possible to unlock pages in a storybook that reveal Rosalina's past. Written and illustrated like a children's book, it portrays Rosalina as a child that finds a lost, abandoned Luma. Wishing to help, she travels into space with it in search of its mama, only bringing her father's telescope and a few supplies. Along the way, they discover a comet with enough items buried in the ice to build a home, and once it's finished, more Lumas appear. The little star creatures begin calling Rosalina "Mama."
Though she's happy to have the Luma as her friends, Rosalina becomes terribly homesick after catching a glimpse of her homeworld through the telescope and the tree under which her mother is buried. The Luma she began her journey with decides to help by transforming into a comet, joining the one Rosalina and the others are living on, and begins traveling in the direction of her planet so that she can return for her desired visit. Surprised by this, Rosalina learns that when Luma mature, they turn into planets, comets, and other celestial bodies.
Having made her home with the Luma as their mama, Rosalina journeys on the Comet Observatory and visits her homeworld every hundred years.
Super Mario Galaxy 2
Rosalina also appears in Super Mario Galaxy 2. In this game, she serves as the key to the game's Super Guide feature, the Cosmic Guide, by taking control of Mario and helping him (and the player) through troublesome parts of the game. Also, she appears at the end of the game where she found her lost Luma and later after the credits, she tells a story to all of the Lumas about the Green Power Stars. The player must collect 120 Power Stars in order to see this sequence.
Mario Kart Series
Rosalina appeared as an unlockable character in Mario Kart Wii. She becomes available for play after attaining a Star Rank in all Mirror Mode cups or, if Super Mario Galaxy save data is present on the same Wii console, by playing fifty races. She races along with a Luma in a kart or bike. In Mario Kart 7, she returns once again as an unlockable driver.
Super Mario 3D World
Rosalina is an unlockable player-character in Super Mario 3D World, available once the player completes Star World 2. She can use a special spin attack akin to Mario's in the Super Mario Galaxy series.
Super Smash Bros.
On December 18, 2013, it was announced via a Nintendo Direct presentation that Rosalina will be a playable character in Super Smash Bros. for Wii U/Nintendo 3DS. She will fight with the assistance of a Luma.