Sheik from OoT. I am fully aware that this character is officially, canonically "just" Zelda in disguise, but back in the day I made up my own headcanon that Sheik is a descendant or at least younger relative of Impa and continues to help Link in Impa's stead while the latter is busy with whatever the sages do in the adult time/age.
If it absolutely has to be an actual canon character, I'd pick Ghirahim. There is something unique and strangely fascinating about that pompous, presumptuous prick. He's the most flamboyant, arrogant, smug choleric in the franchise, hands down. Not even Revali comes close.
