Zostic is the evil alien ruler of the planet Enormous in "Super Morphin Mega Monsters" skits on Sesame Street. Zostic delights in making trouble for innocent monsters (and sometimes, Anything Muppets) on planet Earth, fomenting prejudice, selfishness, and other negative emotions. He has two underlings who carry out his fiendish plots. Like most evil villains, Zostic tends to laugh maniacally; unlike most villains, his maniacal laughter sometimes ends with him hiccupping or coughing.
The character is the equivalent of Rita Repulsa, Lord Zedd, and the other various master villains used in the Mighty Morphin Power Rangers franchise.