Fan Casting Un-Favourite in Sort by Tropes

Where there's an Alpha wolf, there's got to be a Beta. When there is a first banana, there is a second banana. This is the person in the family who can't get a break. For example, this is the child who's the big let-down to their parents, the daughter that was supposed to be a son (or vice-versa), the child the parents had by accident when they'd already decided they didn't need another mouth to feed, the adoptive, foster, or stepchild that came before the parents had a biological child, the illegitimate child conceived by infidelity on the part of one of the parents (if not even worse). But all in all, this is basically the kid who is always getting the short-end of the stick.