“Who? Oh, him.”
“I think he got the "N" in Satan in the wrong place.”
The Crimson King, not to be confused with King Crimson, is a fictional character from The Dark Tower series by Stephen King. Like most of King's villainous characters, (Randall Flagg, Pennywise the Clown) he is built up to be a formidable force of evil but ultimately proves to be an absolute cop-out of a bad guy,
The origins of the malevolent Crimson King are shrouded in mystery but it is said that he was once a Santa Claus impersonator called Nick Oldsaint and worked in Woolworths. However one day he was bitten by a demonic child and transformed into an evil madman. Possessed by an innate desire to wreak chaos and destruction, he created a supervillain alter-ego, The Crimson King.
 He's evil I tells ya, eeeeeeeevil
Rounding up a gang of miscreants that included such prestigious (lol) evil-doers as Randall Flagg, Pennywise the Clown and a vampire who was a rip-off of Count Orlock from Nosferatu called Barlow, he began his quest to ... do something really evil to the universe. It's not entirely clear what his plans were, he was after all insane.
His plan involved destroying The Dark Tower that held the universe together. Not really a pleasant thing to hold the universe together, a dark tower. Sort of screams "Sauron!" but hey, it's Stephen King's story and a dark tower it was. The destruction of said tower would result in the Universe being plunged into eternal darkness (this is somewhat paradoxical, the destruction of something dark, resulting in perpetual darkness but this is Stephen King, he's not really known for logical storytelling).
During a rave however, he choked on a razor-edged spoon (dreadful when that happens isn't it) and died before becoming a ghost and travelling to the place where The Dark Tower was (no, not Mordor). There, he along with a bunch of evil henchmen set up base in a fortress with a much cooler name than Barad-dur (Thunderclap, elegant in its simplicity) where they found a wealth of rubbish technology. At some point he had a son who turned out to be an emaciated half-spider and only actually turned up in the final book but still managed to absolutely twat the shit out of the supposedly allpowerful Randall Flagg before being killed by his other father (don't ask) Roland Deschain in about a paragraph.
 The Final Battle (well, I say battle)
Shortly thereafter, The King tried to destroy The Dark Tower with an army of Carrie's evil psychic cousins. The plan failed (how anticlimactic) and the King tried to take over the tower by climbing onto a balconey where he got stuck, met Noel Coward and was driven even further into insanity by Coward's biting witticisms ("I mean, what sort of evil villain gets stuck on a balconey, I mean, couldn't you have been imprisoned at the core of the Earth or something like that?") and piano playing ("Why must the show go on?" - yes that's probably what most people reading the book are thinking).
Eventually Roland the Gunslinger, Clint Eastwood's mighty cousin, the valiant hero arrived at The Dark Tower for his epic battle with the ultimate evil. Needless to say he was a tad disappointed to be confronted by an deranged, emaciated Father Christmas look-alike lobbing hand-held grenades called Snitches (ahem, sneetches) whilst screaming "EEEEEEEEEEEEEEEEEEEEEEE" but then again, so was pretty much everyone. Noel Coward had buggered off at that point and so was not privy to Roland beating the King to death with a picture of The Scream by Patrick Granville who'd just popped into the story to say hello.
 Theories on The Crimson King
If you're still reading this article, you're probably thinking "What the fuck?" about the title of this section.
Well, Stephen King's fans were understandably a bit puzzled when the satanic character in King's fictional universe turned out to be a senile, grenade-happy old biddy and so they came up with various, mind-numbing explanations as to why this might be.
Some speculated that The King had been corrupted in the past by his future self, stuck at the top of the tower and had then gone and got stuck on a balconey on the tower while he was also at the top, oh and he was also a representative or avatar of Pennywise who actually worked for him and it all gets rather confusing.
Still, others say that he drew power from his minions and the destruction of Barlow, Flagg and Pennywise sapped him of his power, causing him to turn into a bonkers old man. This, amusingly is actually the most plausible explanation (well, second most.)
Others say that The Crimson King was an evil twin of himself from a parallel universe and maybe he was the personification of the evil in Randall Flagg, Pennywise, Barlow, etc and they were really him and AAARRGGHH, my head hurts.
Of course, there is a more plausible explanation for all of this : Stephen King gets turned on by anticlimaxes.
Like I said earlier on, it's Stephen King, he's not known for logical storytelling.