[[caption-width-right:318:Funny you should be so tired, so early in the day...]]
'''''The Demon Headmaster''''' is a book written by Gillian Cross in 1982. The story concerns Dinah Glass, an orphan who's just recently been fostered by the Hunter family. On her first day at her new school, she makes some interesting observations:
* First: All the students are wearing a green uniform. Not only that, but they behave in an oddly uniform manner, using recess to memorise lessons learned in class, and marching around the halls.
* Second: All the students, when asked of their opinion about the school, say "The Headmaster is a marvellous man, and this is the best school I've ever been to."
* Third: There are six prefects (three boys, three girls), who are directly employed by the Headmaster to keep order.
* Finally, when she actually ''meets'' the Headmaster, she learns that not only is he a serious stickler for order, but he also has the ability to hypnotize people merely by looking at them.

Fortunately, she discovers that her foster brothers are incapable of being hypnotized in such a manner, and have formed a group with three other students known as SPLAT (the '''S'''ociety for the '''P'''rotection of Our '''L'''ives '''A'''gainst '''T'''hem).

Following on from the success of that book, Cross wrote a second book, ''The Prime Minister's Brain'', where Dinah encounters the Headmaster again when he tries to access the Prime Minister's computers in the guise of running a computer competition.

The third book, ''Hunky Parker is Watching You'' (aka ''The Revenge of the Demon Headmaster'') follows SPLAT as they become entranced in a new MerchandiseDriven franchise, ''Hunky Parker'' (an "ed-U-cated" pig). Dinah (for once, the only one ''not'' entranced) discovers that the show not only uses SubliminalSeduction, but that the Headmaster is (surprise surprise) behind the whole thing, even going so far as to use a large holiday centre as a sort of sweat shop.

This was followed by ''The Demon Headmaster Strikes Back'', with the Headmaster this time running a Biogenetic Research Centre, which is researching the ability to clone people.

''The Demon Headmaster Takes Over'' follows on directly from the last one, with the Headmaster[[spoiler:'s clone]] developing a computerised brain and then losing control of it.

The final book in the series is ''Facing the Demon Headmaster'', where SPLAT once again run up against the Headmaster, who is this time involved with a new club.

The series was adapted for television by the BBC. The first season was adapted from the first two books, the second from ''The Demon Headmaster Strikes Back'', and the last from ''The Demon Headmaster Takes Over''. (''Hunky Parker is Watching You'' was skipped, and ''Facing the Demon Headmaster'' was published several years after the TV series ended.)
!!This series contains examples of:

* AdaptationExpansion: The second and third seasons of the TV series significantly expand the role of the Headmaster. In ''Strikes Back'' the Headmaster doesn't appear until about two-thirds of the way through the story, and in ''Takes Over'' he isn't seen until the very end.
* AdultsAreUseless / CassandraTruth: A hypnotic Headmaster controlling a school is a claim most [[NotNowKiddo parents would dismiss.]] But even if they decide to see for themselves, they end up getting hypnotized too.
* AntagonistTitle
* AirVentPassageway: During the second half of the first series of the TV show the children break in via the rubbish chute.
** Played straight during their escape from [[spoiler:the fire in Vulcan Tower's control room.]]
* AssimilationAcademy: The Headmaster's idea of a perfect school, unsurprisingly.
* TheCavalryArrivesLate: The British Army arrives at the Biogenetic Research Centre in order to disassemble and to incinerate it, after the events of ''Strikes Again''. Not only do they arrive six months late, but [[spoiler:their visit also causes the reincarnation of the Demon Headmaster... and the resulting ''Takes Over'', and its sequels]]. Seriously...
* CatchPhrase:
** "Got you guessing? That's the way I like it!"
** "The Prefects are the voice of the Headmaster. ''They MUST be obeyed!''"
** "Funny you should be so sleepy so early in the day...your eyelids are getting heavy...you...are...asleeep."
** AuthorCatchPhrase:
-->"We'll go to the police!"\\
"And [[AdultsAreUseless tell them]] ''[[AdultsAreUseless what]]''?"
* CruelAndUnusualDeath: [[spoiler: The Headmaster himself in ''Strikes Back'', where he falls into his Evolution Accelerator machine and gets disintegrated.]]
* EvilTowerOfOminousness: Vulcan Tower, the Headmaster's choice of HQ in ''The Prime Minister's Brain''.
* FourEyesZeroSoul: [[AntagonistTitle Take a guess...]]
* GenreSavvy: Averted with the Headmaster who always underestimates SPLAT and sometimes demonstrated by the children although in a few books they are irritatingly slow to recognize the signature moves of The Headmaster (hypnosis, people acting weird, a new craze).
* HoistByHisOwnPetard: The Headmaster on a couple of occasions.
* HighHeelFaceTurn: Rose in Strikes Again
* InexplicablyAwesome: The Headmaster has [[TheSpook no name or background]] and his abilities are the only supernatural element in the setting.
* HypnoticEyes: Duh.
* JerkWithAHeartOfGold: Lloyd, who is initially a JerkAss towards Dinah but comes to respect her later in the first novel, and looks out for his younger brother Harvey throughout the stories with a natural BigBrotherInstinct.
* LiveActionAdaptation
* MarketBasedTitle: ''Hunky Parker is Watching You'' became ''The Revenge of the Demon Headmaster''.
* MassHypnosis
* MilkmanConspiracy: The Headmaster is rather fond of these.
* MischiefForPunishment: Dinah engages in this to find out what exactly is wrong with the school.
* OperationBlank: In the TV series, the Headmaster names his Master Plan as...[[ShapedLikeItself MasterPlan]].
* OutGambitted: "''You cannot beat me. I think you will find that I am always a step ahead.''"
* ShowWithinAShow: ''The Eddy Hair Show'', ''Hunky Parker'', ''APE!'', all of which are plot-relevant.
* SmugSnake: The Headmaster, on multiple occasions.
* SpannerInTheWorks: The Headmaster should take more notice of Dinah's capabilities. The TV version is a bit more GenreSavvy, and programs the computer at Vulcan Tower not to admit anyone called Dinah Glass; unfortunately for him, Dinah has changed her name to Dinah Hunter by that point, and the computer doesn't pick up on it.
* StalkerWithATesttube: A decidedly non-romantic version: [[spoiler:the Headmaster employs Dinah's father at the Biogenetic Research Centre, so he can steal Dinah's DNA and create Eve, a human/lizard hybrid.]]
* SubliminalSeduction: "Hunky--or nothing!"
* TeenGenius: Dinah
* TeamMom: Mandy
* ThemeTuneCameo: A chiptune rendition of the TV show's theme can be heard in the background of the ''Octopus Dare'' game.
* ThisIsUnforgivable: Inverted, as it is the Headmaster who says this to S.P.L.A.T.
-->''"Next time, I shall win! And I shall NOT forgive you!"''
* TransferStudentUniforms: Dinah wears her old school's uniform on the first day.
* WellIntentionedExtremist: The Headmaster (at least, that's what he'd have you believe). He has no interest in money and just wants a world of perfect order and efficiency - at the cost of all emotion and curiosity.
* WeWillMeetAgain: See ThisIsUnforgivable above