Fear, my favorite emotional state. --Windom Earle
Warning: Here be spoilers.
Windom Earle, played by Kenneth Welsh, is Special Agent Dale Cooper's former partner, now gone batshit insane. He comes to Twin Peaks seeking two things: The power of the Black Lodge, and Cooper's death.
Earle and Cooper worked on a case together in Pittsburgh where Earle's wife Caroline was a material witness. Cooper was assigned to protect Caroline, but fell in love with her instead. But he let his guard down, and Caroline was killed. The incident ended with Earle in a mental hospital, and a guilt-stricken Cooper vowing never to allow emotions to interfere with his professional life again.
The first hint of Earle's existence in the show comes in episode ten, when Albert Rosenfield tells Cooper that Earle has escaped from the institution. This gun doesn't go off, however, until episode 13, when Cooper's superior Gordon Cole gives him a note which turns out to be a message from Earle. It is a chess move; Cooper and Earle used to play chess when they worked together, and Earle never lost. Cooper realizes immediately that this game is serious, and enlists surprise chess whiz Pete Martell's help in planning his response.
The game is played out through notices in the classified ads, but it soon becomes clear that no amount of chess skill will appease Earle. In episode 18, Cooper receives a cassette tape in the mail, with a recorded message:
Of course you couldn't help but take note of my
emphatically traditional opening. I must say your
responding move was nothing if not reflective of your
predeliction for the tidy and fastidious. See how my
response to you begins to lead us towards a classical
confrontation? But there's doubt in your mind: what are
my true intentions? How will you answer this time?
Hobgoblins, Dale; consistency, predictibility, giving rise
to patterns. We both know only too well how these
patterns leave you vulnerable to attack. You with your
wounds. I with mine. Let me paint you a picture. My
knights will skirmish. Lanes of power and influence will
open to my bishops and rooks. Pawns will naturally be
forfeit. I'm even prepared to sacrifice my queen because
I assure you, dear Dale, my goal will be attained at any
cost. The king must die.
Sure enough, Earle soon begins
sacrificing pawns -- real people, who are pawns in his
vendetta against Cooper. The first is a drifter, found in the back of the sheriff's office with a pawn
taped in his mouth. The second is a local kid, played by
Ted Raimi, who is found stuffed into
papier mache pawn in the
gazebo. And soon, Earle begins choosing a queen, sending
poetry to the town's prettiest girls to encourage them to enter the
Miss Twin Peaks competition. The winner will be his queen, and his bait for Cooper.
During Earle's planning and plotting stages, he skulks around the town in various disguises, coaxing information from the residents. He also manages to enslave brain-damaged, barely-functional Leo Johnson, and capture and drug Major Garland Briggs. Not only that, but it comes out that it was he who killed his wife Caroline in Pittsburgh, and that his subsequent madness was faked (with high doses of Haloperidol) so that he would not be suspected. As Earle heads off to watch the beauty pageant, he leaves Leo trembling under a box of tarantulas which will fall on him if he moves. Truly a charming character.
Earle, with his "queen" (Cooper's love interest Annie Blackburn -- Earle rigged the contest), manages to lure Cooper into the Black Lodge, leading to the weirdest scenes in the entire series. Earle is hoping to control the power of the Lodge, but we never see whether he makes it out -- it's possible that he ends up trapped. Cooper certainly comes out worse for wear... but that's for another node.
Windom Earle is perhaps the scariest character in Twin Peaks, because unlike the other major evil entity (Killer BOB), he is a real person. There's something less unremittingly frightening about someone who's evil because he has no other choice. When Cooper and Sheriff Harry S. Truman discover Laura Palmer's killer, they have the following exchange:
TRUMAN
I've lived in these woods all my life. I've heard some
strange things. Seen some too. But this is way off the
map. I'm having a hard time believing.
COOPER
Is it easier to believe a man would rape and murder his
own daughter? Is that any more comforting?
Windom Earle is a deeply frightening character because he embodies real-life human psychosis, not fairy tale evil. He is more like the man who would rape and murder his daughter, and that's a type who's all too familiar. It's not more comforting at all.