Kobolds

Overall, the most common traits are:
* Short stature, comparable to a 7-12 year old human
* Humanoid form
* Brownish to black coloration
* Hairy
* Large ears, often pointed
* A tail ending with a tuft (somewhat similar to a donkey's)

Kobolds are often depicted more mischievous than malicious, though this is unreliable.

D&D is notable for turning kobolds into dog-like and later into reptilian-like beings, though they were still short humanoids.