and The Incredibles' Mom - Elastigirl
Oops...I mean Helen Parr...
As we watched Big Hero 6, we both couldn't help but think of The Incredibles. Helen & Cass seemed so similar in so many ways - the big eyes, the hair, their voices were slightly similar, and their sense of humor. It turns out in our theory, Helen Parr AKA Elastigirl, is actually Aunt Cass' sister. The superhero nature just runs in their blood, apparently. Helen and Cass had a brother. Their brother was Hiro & Tadashi's father.
Although it seems like it would've been a wise decision to send Hiro & Tadashi to live with the Parr family AKA The Incredibles seeing as how they already had 3 kids, Hiro's father & mother made the decision that if anything were to happen to them, they'd want his sister Cass to take the kids, in order to keep their kids from the life of crazy antics and super-villains, and to get them the education they would need to make the world a better place.
Also, Elastigirl does exist in some form in their dimension as there is a figurine of her in Fred's room. Which is certainly, as we know, because he is a big fan of fictional and real life superheroes.
Hiro was just a toddler when his parents died, and since super-heroing and super-smarts just happened to be in his blood, he had no choice but to create a team as amazing as Big Hero 6, following in the footsteps of his Aunt and Uncle - The Incredibles!