In fiction, baldness often equates with lack of moral fortitude. Many, many villains are recognised as such by the audience by their shiny, shaven noggins. It might be the Corrupt Corporate Executive in a political thriller, the sinister evil sorcerer, unholy priest, cult leader, or Evil Overlord in sword-and-sorcery, or a thuggish Giant Mook readying to crack the hero in two. However, it is most commonly applied to the Evil Chancellor and the Mad Scientist.
Where the hero has his flowing golden locks or a boyish, tousled mop of red or brown hair to indicate his youthful purity, something about the complete absence of hair makes a bald villain look particularly nefarious, especially while he's slouched on his throne, steepling his fingers and delivering a Breaking Lecture while the ominous backlight shines off his gleaming chrome-dome.
This might be a throwback to ancient belief in hair as a symbol of health and virility, as exemplified by the Biblical story of Samson; it may also be more primal still, as a shaven head more closely resembles a skull and, combined with the natural tendency for us to lose our hair as we grow old, is therefore symbolic of aging and death. As a matter of fact, in ancient Rome, baldness was considered a gross deformity. Somehow, that didn't stop the very bald Patrick Stewart from being called "The Sexiest Man on TV" in 1992.
Whatever the original reason, Hair Hates Evil, and about the only times you'll see a kind and moral character without his (or her) hair will be when it's an egg-headed Smart Guy (who's probably also in a wheelchair), a Buddhist monk, a Bald Black Leader Guy, or the Littlest Leukemia Patient.
The only other good guys who go shaven are BadassAnti Heroes, so if a hero shaves his head as part of an Important Haircut, it is a sure sign he's about to get Darker and Edgier.
The tendency is, indeed, for the moral decay of a character to be inversely proportionate to the length of their hair, with innocent, virginal princesses practically drowning in their romantically flowing locks while the hard-bitten Badass sports a spiky military crewcut. The most frequent aversion of this trope is the White Hair, Black Heart, whose usually long and luscious tresses exist as a symbol of his evil, not in spite of it.
For the ultimate combination, supply a bald villain with a villainous goatee. This trope is also a function of Good Hair, Evil Hair.
Taking this trope way beyond its logical extreme, occasional verymadscientists will also shave off their skin and the top of their skull, leaving their brains completely exposed.
For aversions, see Bald of Awesome.
Nearly all of the major villains have no hair: Pilaf, both Piccolos, Frieza, Cell, Majin Buu. They're not exactly bald, though, they just have no hair — with the possible exception of Pilaf, none of them are mammals.
Plenty of bald heroes too: Tenshinhan, Krillin, and Master Roshi. But Tenshinhan was originally a villain (albeit one who almost immediately performed a Heel-Face Turn a few eps after his introduction), so the point stands.
Krillin originally convinced Master Roshi to train him by bribing him with pornography. And Krillin isn't naturally bald, as he grows his hair back (as a sign that he was no longer living as a monk who renounced all worldly pleasures) after marrying Number Eighteen.
Toriyama might be playing with this a bit. Tenshinhan is a bald villain, but becomes a good guy when he finds out people respect it more. Nappa was a classic "bald" villain (and a classic villain in many respects), but gets trumped by the true hero in mere seconds and replaced by a preferable, haired antagonist.
Lordgenome. Also has the Anti-Hero goatee. And epic chest hair. And his scalp catches fire when he does awesome things such as beating the crap out of mechas with his bare hands.
Even The Anti-Spiral fits this trope.
Ivan the Terrible (or Ivan of Russia, in the Japanese version) from Giant Robo: The Day The Earth Stood Still is bald, though he's not the most nefarious of the evil group he's a part of, even though he may be one of the biggest nutcases in the entire anime. Though, to be fair, one of the guys dead-set on doing good is bald as well.
All over the place in Bobobo-bo Bo-bobo. The Big Bad is Czar Baldy Bald IV, head of the Chrome Dome Empire, and his Mooks are generally bald as well.
Both played straight and inverted in Kinnikuman. Buffaloman, originally introduced as the most powerful Devil Superman in the series, reveals himself to be bald in the following arc. However, the reveal only happens when he officially pulls a Heel-Face Turn.
Vargus, who was initially introduced as a thuggish bully of a Giant Mook that attacked Negi in the Magic World for no reason, though it's later shown that he's actually a lot nicer than he first appeared.
There's also the leader of the Bounty Hunters later on, but he is more of a Punch Clock Villain; he meets Negi in a bathhouse later "off the clock" and comments that he has no intention of pulling anything.
GaoGaiGar: In FINAL, Palparepa, the lead protagonist's evil counterpart, is completely bald.
In Legend of Galactic Heroes, three morally questionable characters are bald. (Though most morally questionable characters are not.)
The evil school inspector in Gokusen. Some villains can make their Scary Shiny Glasses gleam menacingly; this man creates the same effect with the top of his head.
In order to illustrate their pre-series Face-Heel Turn, Tokyo Tribe 2's Mera and Skunk both shave their heads. Kai even comments on Mera's shaven head before he becomes aware that he's one of two people that Mera vowed to kill.
Inverted with the Kongo twins in Eyeshield 21. Unsui's baldness is meant to reflect his monk-like attitude and is a generally swell guy. His brother, on the other hand, has a huge mane of dreads and is a total jackass. In fact, Agon shaving his head is seen as a mark of improvement in his character.
Kriem when she appears in Episode 18 of Tiger & Bunny. It makes sense, really, when you consider that her hair enables her to control inanimate objects to wreak havoc. The hospital staff probably shaved her head so that she wouldn't be able to when she woke up.
In the Ace Attorney manga, Robin Wolfe has a bald head that is quite shiny and catches Maya's attention as soon as they meet. The "evil" part comes when it turns out he called an arachnophobic employee to his home, restrained him in a chair in a guest house full of spiders, and left him there for hours, leading him to be Driven to Suicide.
In Apocalypse no Toride, the main baddies at Shouran are all bald;Hitotsukabuto Kiyoharu and Nakazaki Hitoshi and Kyouichi.
Naturally, this has had fun poked at it several times, such as by Larfleeze during the events of Blackest Night. Also, in an episode of Justice League, Lex, accompanied by Supergirl and Steel, revealed that he had a secret laboratory... fronted by a barbershop.
Steel: Gotta hand it to you, Luthor; nobody would think to look for you here.
The funniest thing is Luthor wasn't originally bald. He was actually an Evil Redhead until someone drew him without hair.
Shazam villain Dr. Sivana (who predates Luthor by a couple of months) is another bald mad scientist, who is also diminutive, gangly, ugly, and wears coke-bottle glasses. He has a thing for talking worms.
Remember Archie Comics' own super hero imprint? Well, a recurring super villain dubbed the "Brain Emperor" introduced in the original "Mighty Crusaders" becomes the Big Bad in New Crusaders.
Marvel Universe semi-aversion: Moondragon, even when she was not being actively influenced by the malevolent monster she named herself after, fit The Gift trope to a tee. Her girlfriend Phyla mellowed her out, some.
Tintin encounters badguy Rastapopoulos on several occasions.
Also, recurrent conspirator Jurgen is short on hair, though he has some on the top of his head.
Gold Digger's Zelda — a genetically engineered mook to an evil (but he's getting better) child genius — has no body hair at all, not even eyebrows (or possibly eyelashes). She hates it (she used to have very long and luscious hair). It's explained as the result of having "Dolphin DNA" being used in her gengineering.
Many Sin City villains have this going for them: Manute, Wallenquist, Liebowitcz, Cardinal Roark, and the Yellow Bastard. There was also an evil rich guy with an odd sense of family values in the short story Daddy's Girl.
Depending on how you view his "anti-hero" antics, the New52 version of Superboy is this when fresh out of the test tube.
In the original Flash Gordon comic strips, Prince Barin sported a clean-shaven pate in his first appearances — but when he did his Heel-Face Turn, his hair grew out with astonishing rapidity. Ming, however, is bald as...someone who is bald.
In The Phantom, many baddies sport bald pates. In General Tara's case, it is possible that the baldness is a choice to indicate virility, since he augments his intimidating dome with a large bushy handlebar moustache (gleamingly waxed) and matching goatee. To indicate his self-indulgent lifestyle, the fat buffoons in the Phantom strips (Tara included) always carry an extra bulge of flab at the base of their shiny skulls.
Charles Addams' depiction of Uncle Fester in The Addams Family is utterly bald, without even eyebrows. Like most of the Addams characters, Fester is a bit more on the "demented" side than actually "evil" per se.
The two main antagonists in Iron Man 1, as fate would have it, are both bald. Reportedly, Jeff Bridges leaped at the opportunity to shave his head. As if to make up for this, it has two good bald characters.
After the events in Star Wars: Revenge of the Sith, both Vader and Sidious are bald. As was Maul. (In Maul's defense, his entire species is bald, and not all of them are evil.) Conversely, most of the Jedi have long hair.
The main character Pink in The Wall is on a downward spiral of insanity from the beginning of the film, but when he really loses it and envisions himself as a Nazi-like tyrant, he shaves everything: face, head hair, body hair, eyebrows, nipples...everything!
The Nazi consul (played by Otto Preminger) in Margin for Error.
Voldemort in Harry Potter is bald. In the first film, Quirrell was also bald.
Voldemort in Harry Potter, to play up the whole reptile angle. To be fair, in his case, Voldemort was so far gone from anything remotely human that having hair at all would have been an accomplishment.
Something of a subversion: Matilda's father (who has plenty of hair and happens to be unscrupulous) believes that smart people have good, strong hair and that, therefore, bald people are dumb. (Matilda points out that William Shakespeare was bald.)
Harap Alb, a Romanian folk tale, has "Spânul', "The Bald Man", as the primary Sadist villain. The main character is told that the only thing worse than a bald man is a red haired one...Guess whose daughter he is forced to win over later?
Although he was not described specifically in the stories, Sherlock Holmes's Archenemy Professor James Moriarty was presented as being bald in the earliest illustrations of the character. In many later illustrations, he just has a very badly receding hairline, which also makes him look more professorial.
Rare female example: in Ian McDonald's Desolation Road, Arnie Tenebrae becomes a psychotic, sadistic warlord. At one point, it's mentioned: "She was busy shaving her head."
The title character in the A-to-Z Mysteries book The Bald Bandit, who steals from a bank.
Sadi, one of the evil eunuchs at Salmissra's court in The Belgariad. In fact, most Nyissans shave their heads, if for no better reason to keep out the lice. In The Malloreon, Sadi allies with the heroes, takes a level in badass, and graduates to Bald of Awesome. Even in the Belgariad, by about midway through when Sadi no longer stands to gain anything by opposing the protagonists, having him as the de facto ruler of Ny-Issa is about as welcome a development as could reasonably be hoped for (and certainly better than when Salmissra was in charge in any meaningful way).
In Blood Meridian, the monstrous giant Judge Holden is utterly hairless, lacking even eyebrows and eyelashes.
Speaking of Patrick Stewart, he's the Big Bad in The BBCJohn le Carré serials Tinker, Tailor, Soldier, Spy and Smiley's People. When playing the villain in I, Claudius, however, he's got hair — either for the above-mentioned 'deformity' reason or because his bald head had not yet become famous.
Rare female example: as Battlestar Galactica's president Laura Roslin loses her hair to cancer treatments, she also becomes increasingly totalitarian.
Black Hole High: Victor Pearson, the series' antagonist, is bald in the present day, but in the 1987 time zone, he has a full head of hair. Almost everything we see of him in this period is sympathetic. He also manages to keep his hair in an alternate timeline where he's a slightly dotty science teacher. The final kicker: in the series finale, which reveals Pearson's ultimately noble motives, Victor is starting to grow his hair back.
The Technomages of Babylon 5 all shave their heads, for easier access to the brain and spinal column. Their evilness varies from person to person.
Vic Mackey, of The Shield, though YMMV for how evil he is.
In an episode of Honey, I Shrunk the Kids: The TV Show, Nick gets affected by one of Wayne's experiments, giving him the ability to suck other peoples' intelligences. As he becomes more intelligent (and evil), he develops an overly large, bald head.
Walter, Mike, Gus and the entire Salamanca family from Breaking Bad. Walt's is an Important Haircut shortly after he starts taking treatment and his hair begins to fall out anyway.
Walter Junior: (seeing Walt bald for the first time) Badass, dad!
Jesse: (ditto) You look like Lex Luthor.
In Game of Thrones, the Token Evil Teammate of the good guys' side, Roose Bolton, has a receding hairline, instead of his way more over-the-top villainous appearance in the books which included more or less every possible visual cue aside from baldness.
WWE wrestler Kane became bald when he lost his mask in a match. By no coincidence, this is also when he started getting really, really evil. Like, cackling horror-movie-villain evil.
King Kong Bundy was the greatest example. Apart from his eyelashes, he was completely hairless.
Genki Horiguchi of Dragon Gate calls himself H.A.G.E of Evil (hage is Japanese for bald).
The Straight Edge Society in the WWE is a whole stable of these. Inverted in the leader, CM Punk, whose mane is the whole selling point of the gimmick... Punk lost to Rey Mysterio at Over the Limit 2010 and got shaved bald, but it's averted(?) in that he covered it up with a black mask.
This even shows up in Adventures in Odyssey, a radio show. For a long while during the Novacom saga, Mr. Charles was informally known as "the bald guy."
Mark Kermode and Simon Mayo even made up a rule about it (when reviewing Prince of Persia).
Played with in the 2nd Edition art; the "Ultraviolet-Clearance" section contains pictures of a "typical GM", an evil-looking robed fellow who is usually seen cutting up the rules or cracking a whip and is completely bald.
The generic High Programmer depicted in the art of the original edition likewise bears more than a passing resemblance to Uncle Fester of The Addams Family.
One of evil magocracies of Forgotten Realms is Thay, where ruling Red Wizards (both men and women) has shaved and tattooed heads. This tradition was questioned when Lauzoril (the most charismatic leader there) ignored it and broken when traditional power structure was smashed by internal strife.
Artwork of various Chaos leaders, especially sorcerers, in Warhammer 40,000 usually portrays them as bald, with various Chaos symbols worn on the scalp.
Star Trek Online gives us Colonel Hakeev, a senior officer of the Romulan Tal Shiar and Big Bad of the Romulan storyline. Obisek, leader of the Reman Resistance, plays this earlier on, but averts it when it's revealed that he and the player are working towards the same goal.
Moebius, servant of the Elder God, is a conniving manipulator who eschews hair of any sort and is notably bald even in thousand year old murals depicting his younger days when he led the rebellion against the vampires who ruled over humanity in the past.
Minor characters Azimuth and Marcus, both antagonists, are also bald.
The Helghast in the Killzone series are all bald. Apparently, this is a side effect of having emigrated to a Death World.
Mr. Big from the Art of Fighting series: a crime boss who kidnapped a teenage girl to blackmail her father and force both her brother and her best friend to fight him.
Both Sarevok of Baldur's Gate and Jon Irenicus of Baldur's Gate 2 had shaven heads.
Bitores Mendez, one of the villains of Resident Evil 4, was both bearded and bald. In fact, he looked a lot like Rasputin.
StarCraft: The Dark Templar was a definite subversion. On the first game, they were largely regarded as a bunch of dark, shady heretics. One of their defining traits is that they don't have tendrils on the backs of their heads (the protoss equivalent of hair), making them essentially bald. Zeratul is the most obvious example. It turns out that they are actually one of the most heroic characters in the game. This, in turn, makes the Dark Templar a straight example of Important Haircut, but not Bald of Awesome.
In Metal Gear Solid 2, we have Fatman, who, aside from, well, whathe is named for, is also bald (the script implies that his baldness is the result of severe burns). Similar to Coldman, he is a very horrible person.
Richard from Looking for Group is most likely bald, since one statue depicting a hoodless near-lookalike of him was bald, a glimpse of him having his head healed didn't show any indication of hair, and an early page where we see an x-ray version of Richard didn't show any hair outlines. Also, we get a few "up-hood" shots, and the fact that the scarily-similar Sisters have little-to-no-hair themselves does not help matters.
Freakshow of Danny Phantom. Arguably, his whole outfit has a villain look, but when surrounded by Goths, not so much.
Baron Ünterbheit in The Venture Bros.. The show, however, also subverts this trope in that Rusty Venture is bald and Brock shaves his head at the end of Season 3. On the other hand, it might not be so much of a subversion, when you consider the fact that it would be difficult indeed to ever see Rusty or Brock as anything close to being GOOD - one's a Jerkass and the other is a Sociopathic Hero.
In Iron Man: Armored Adventures, Obadaiah Stane's baldness carries over from the comics, down to being conspicuously clean-shaven when compared to Jeff Bridge's recognizable beard from the film. His head of security, O'Brien, is also bald. He carries it well.