Dragons.

Majestic, magical creatures, strong and wise.

Well, mostly wise, as they age. Some young dragons are as headstrong and foolhardy as any teenage human who ever walked the earth. The reasons for this are quite obvious, with a bit of thought. Take your average teenage boy, with a teenage "rebel against the world" mentality. Now, give him armored skin that only a sharp sword has any hope of penetrating. Then, as if that weren't enough, give him wings, to soar over most any earthbound obstacle, and you will start to get an idea about how dangerous free young dragons can be. As for the fiery (or otherwise elemental) breath, most do not develop that aspect until they have reached a more responsible age (thankfully).