Evil TransFormer, a member of the dominant evil faction in TransFormers
Generation 1 and several other series. (Known as Destrons in Japan; converted into Predacons for the Beast Wars series).
Most stories suggest they began as a rebel faction on Cybertron which invented arms for the first time and sought to control other transformers in order to dominate the universe, although I find it more likely that they were actually the dominant faction from the start which gradually became more and more arrogant as their power increased. (This is more consistent with the fact that the Decepticons are in control and the Autobots are the rebels in nearly all the early TransFormers stories set on Cybertron).
Hell-bent on interstellar domination, including on earth where they crash-land, the Decepticons attempt to seize and amass energy when and wherever they can, without any concern for other beings or for sustainability. Many Decepticons are also depicted as ruthless and malevolent entities in their own right, enjoying destruction and violence as a good in itself (although the attribution of such emotions to robots seems problematic).
The Decepticon symbol is a
purple face insignia looking similar to
Soundwave's head. In the cartoons, they also always fire purple/magenta laser beams.
Led by Megatron and later by his reincarnated form,
Galvatron; also in various media by other characters such as
Ratbat, Soundwave, Starscream,
Scorponok, Bludgeon,
Thunderwing and Lord Straxus.
Example:
"The
Decepticons are
blitzing Autobot City. We're really taking a pounding. I don't know how much longer we can hold out" - Blaster, in TransFormers: The Movie.
George W. Bush is intent on a Decepticon-style oil grab in the Middle East.
That van is painted in a very scary way; it looks almost like it should be a Decepticon.