I'm a huge fan of the theory that Rosalina is the daughter of Lady Timpani and Lord Blumiere from the Paper Mario series.
The quickest summary I can write is there are coincidences that Timpani and Rosalina share. A major point is that both depictions of their home involve a tree on a hill and them residing in a place where no other beings are mentioned to exist beyond their own family-- Timpani with Blumiere and Rosalina with her father, mother and brother, respectively.
The second major point is Dimentio's promise of a 'shadow' that would seek to destroy all worlds after his demise in Super Paper Mario
, which would likely be the cause of Timpani's death in Super Mario Galaxy
-- and while it couldn't destroy the paradise created from the Purity Heart, it's very likely this was the destruction of Rosalina's 'world' in childhood. [This can get confusing if you don't know the plots from different games, but it's worth noting!]
And the third major point would be the Tribe of the Ancient's knowledge that darkness, ultimately, can't live without light. The Shamans from the Mario series understood this information from the [Dark] Prognosticus, whose owner is almost certainly the late Dimentio himself. Hence, it's likely Rosalina exists as Dimentio's failsafe to provide the light that will battle the source of evil that will enter every Mario story, regardless of who the protagonist/antagonist may be.
But hey, like I said, this is all just a theory. It's just really
cool to me.
Along with Rosalina, I added Dimentio, the seven Star Spirits, Twink, Tribe of the Ancient Four, and Geno (who I designed differently because his game depiction is just Gaz's doll from Super Mario RPG-- so this is how I imagine a Star Warrior would look like to serve Rosalina). And for personal kicks, I chose green for Geno's hair to connect the mystery of Rosalina's brother (in Rosalina's storybook, her younger brother is depicted with mint-green hair). Still kept certain features like the key symbol on his armor, and the line on his face that his toy form had. :]
Man, these characters are definitely tops on my list of favorites. Sometimes I wish the Mario games would flesh out more of their back-stories, but at least it gives us wiggle room to imagine possibilities.
More Geno and Mallow later on!
Tribe of Ancients www.mariowiki.com/Tribe_of_Anc…
Star Spirits www.mariowiki.com/Star_Spirits
Lady Timpani www.mariowiki.com/Tippi
Lord Blumiere www.mariowiki.com/Count_Bleck
Timpani & Blumiere's Ending www.mariowiki.com/images/a/ae/…