Films: Men in Black (1997), Men in Black 2 (2002), Men in Black 3 (2012)
Alias: Mikey, Edgar the Bug, Serleena the Kylothian, Jarra, Boris "the Animal" the Boglodite
Location: Eldritch location/Haunted home/Civilized Area
Height/Weight: Ranges from half that of an average human (Jarra) to that of a large building (Serleena)
Summary: When people talk in hushed words about secret organizations like the Illuminati or, ironically enough, the Men in Black, it is often words of scorn and distrust. Who would trust an obstensibly government-operated group of dubious aims? But in the case of the guys in dark suits and fancy gizmos, you needn't worry. They have their off days, but they have our best interests in mind. That, and the interests of every other being in the galaxy.
History: For as long as people have been even aware of aliens, the Men in Black have been surveying the world in secret. Their goal is to provide sanctuary for most aliens, and exterminate those who would use their abilities for evil. And ever since James Darrell Edwards III, AKA Agent J, got into the business, or at least went from rookie to professional, there has been an impressive rogues gallery. We got Edgar, a monstrous insectoid bent on creating war between Earth and another race and feeding on the corpses that remain alongside his brethren. There's Serleena, a horrible monarch whose connections with the MIB run deep. And then there was Boris the Animal (IT'S JUST BORRIS!!!), the last of a tyrannical race that he tried to bring back via time travel.
Notable Kills: Edgar gets his human disguise by tearing off a farmer's skin, Serleena swallows a mugger whole before spitting what remains out, and Boris holds the dubious honor of killing J's dad, thus setting him on the course to becoming an MIB agent.
Final Fate: Edgar is blown apart twice by both an MIB agent and the very same woman he was interrogating, Serleena gets blasted to holy hell by J and K after failing to stop another alien from fulfilling her destiny, and both past and present Boris are destroyed when the former is vaporized by K and the later sent hurdling to his death (and vaporized by spaceship fire)
Powers/Abilities: Edgar can fit into any disguise, Serleena can simply mimic any imagery as well as utilize almost instantly fatal tentacles to rip and/or take over bodes, and Boris has a symbiotic relationship with a bizarre arthropod that fires an infinite amount of razor-sharp spikes.
Weakness: Anything conventional, or at least the tech that the MIB have access to. Also, Edgar is easily pissed by the act of killing insects.
Scariness Factor: 4-Oddball CGI notwithstanding, these are some pretty devious aliens with a varying case of fright for all. Edgar is straight up unpleasant (especially when fiddling with his disguise), Boris looks like a homeless biker from Hell (to say nothing of his true form), and Serleena is perhaps one of the most powerful and deceitful of them all, taking out swathes of MIB agents and capable of turning into something gigantic and almost invincible. But then of course, the MIB always finds a way.
Trivia: -An animated series based on the first movie was aired in 1997. It expanded a bit on where Edgar's failure left off, with the rest of his kind, led by their queen, tracking down his killers to execute them personally.
-Part of the reason that Will Smith and Tommy Lee Jones' dynamic worked so well in the first film was that the latter was gravely disappointed in the script he was given, so while he was ad-libbing most of his lines, Smith was trying to keep pace. Because Smith was playing the new recruit, it worked rather well.