The Ferengi were first mentioned in the very first episode of Star Trek: The Next Generation: "Encounter at Farpoint". They were regarded as a species of fierce, bloodthirsty Mafiosi known to eat their former trading partners. Their early appearances bore this out -- the Enterprise crew's first several encounters with the Ferengi were violent, and the Ferengi were often better-armed. Early on in the show, these short, orange-skinned, sharp-toothed aliens were a suitable replacement for the pacified Klingon Empire as the chief threat to the Federation's peace.
Linguistic note: The name "Ferengi" is an Indo-European word meaning "alien" or "foreigner". From it comes the word "Varangian", which was the Byzantine Greek name for the Vikings -- history's archetypal raiders-and-traders. (The Russians called the same people "Variag".) Arabic can play, too; see "Ferengistan".
Over the course of ST:TNG
, the Ferengi became less fierce
and, instead, increasingly sleazy
-- in personal matters as well as financial. This process seems to have culminated in certain chunder
-inducing scenes of Lwaxana Troi masturbating
a Ferengi captain's earlobe
s. By the beginning of DS9
, the pacified Ferengi had been completely replaced by the Cardassian
s as the "threat species", and could now be played for comic relief