Calvin O'Keefe is one of the main characters in A Wrinkle in Time by Madeleine L'Engle, and he is extraordinarily connected to the Murry family. He is uniquely suited to be linked to this particular family, as he is a genius and an athlete who has the ability to "kythe"--communicate through a kind of mental telepathy.
Calvin likes Meg Murry, the only daughter in the family, but he is most like Charles Wallace Murray (though Calvin is much "cooler" that Charles Wallace in society's eyes). The two of them have a unique connection which allows Calvin to eventually save both Charles Wallace and Mr. Murry from IT.
Calvin likes the Murrys, despite their oddities, because they represent all the things he does not have in his own family life.
Calvin O'Keefe: Your family, you're all... something... I don't know what.
Meg Murry: We're mostly just ordinary.
Calvin O'Keefe: No, I don't think so. Not as ordinary as you think.
The Murrys welcome Calvin, and he is happy to be part of them. Because of his unique connection to each member of the Murry family, he is able to save them from IT and himself from a rather loveless, lonely life.