Smoke

Smoke is the main antagonist of the educational cartoon special/crossover known as Cartoon All-Stars to the Rescue - which has become a somewhat infamous example of anti-drug propaganda and had a host of many characters from varied children's media band together in order to try and stop Michael, the main protagonist, and his use of drugs, which is slowly tearing his life apart. He is voiced by the late George C. Scott.

However Smoke is intent on making the main protagonist a drug-addicted wash-out and malcontent, he may well be an evil ghost or demon or even an embodiment of drug abuse itself (he is definitely not human and seems to be obsessed with spreading evil, further suggesting a demonic origin).

Smoke is eventually defeated (by Michael refusing to listen to him any longer and throwing him into a garbage truck) but vows to return someday, whether or not he will is unknown and like many villains from crossover events he is considered a "one-shot" encounter and will likely not be seen again unless they ever make a sequel (which seems rather unlikely).