Dragons
A dragon, but not the way you think. In Poland, where I live, there’s one story of a dragon that nested under the hill called Wawel in Cracow and demanded to be given food. Otherwise, he would kill people. The dragon was eventually tricked into eating food poisoned with sulfur (and, according to the sources, exploded, but that’s not important). The story, while it used the Polish name for a dragon (smoke), never mentions any dragon-like features – not wings, no fire breath, no scales, etc.
What I believe (I’m no historian, just a history nerd) is that the dragon in this story was actually human. He could freely communicate with other humans to threaten them but was somehow seen as someone very dangerous, someone inhuman. It could have been a serial killer or a one-time murderer cornered into the cave who used his aura of dangerousness to try to buy some time while he looked for a way to escape. It could have been a person shunned by society for some mental or physical deformity who tried to make the best out of a bad situation. I believe that Grendel, Grendel’s mother, and the dragon from Beowulf’s story were also human.