Rikki-Tikki-Tavi from The Jungle Book
Rikki-tikki is "eaten up from nose to tail with curiosity," and this curiosity allows him to learn just as if he had a mentor figure to teach him (7). His fighting skills are also naturally "inherited from his family" (35), and he knows a "mongoose's business in life [is] to fight and eat snakes" (25). In other words, Rikki-tikki doesn't need a Merlin character to tell him to go fight the dragon, because he's going to do it anyway. That's just how he rolls.