Imp

The imps are a mischievous and nefarious race of small, fiendish creatures. They are granted to the Legion's warlocks as familiars. Although their frames are tiny, they are able to store tremendous amounts of fel energy.

Speculation
It is possible, based on the body structure similarities, that imps were evolved from the Grell species. In which case, they were evolved into demons during or after the War of the Ancients, much like how some elves were evolved into Satyrs.

Myth

 * An Imp is a mythological being similar to a Fairy or Demon, frequently described in folklore and superstition.

Trivia

 * All Imps are afraid of rainbows.