"My garden's full of pretty men, who couldn't stay away..."
— Heather Dale, Medusa
Originally a character in Classical Mythology, Medusa has taken a life of her own, and now exists in all kinds of fantasy — sometimes as a person, sometimes as an entire species. Medusa's main characteristics are snakes for hair and that people turn to stone just by seeing her face. Oh, and don't look at the illustration!
In almost all versions, Medusa is fully humanoid and Always Female. In some versions, her hair-snakes are venomous. In others, they are not literal snakes but rather hair that supernaturally behaves as if it were made of living snakes. When a version contain a male Medusa, it's usually some Spear Counterpart with some other name.
The oldest story known to feature Medusa is the adventures of Perseus. In this story she is merely a boss monster whom Perseus defeats by decapitating her (and later using her head to petrify enemies) without looking at her — he sticks to looking at her shadow or looking through a mirror, depending on the version.
Myths and stories with background for Medusa was added later. There are two different such prequel myths regarding the origins of the original Medusa. When Medusa is used in fiction as a unique being rather than as a species, she is typically given either one of these two origins, or no origin at all.
One origin is that she and her fellow Gorgons was simply created/born that way. In this origin, the Gorgons are typically three sisters, the other two being Stheno and Euryale. The Greek word "gorgon" means "horror". Besides having serpents for hair, the Gorgons were described as having tusks, brazen claws, and wings; in a few very early depictions they are shown as quadrupeds, possibly because Pegasus was born out of Medusa's blood when she was beheaded by Perseus. Note that the Erinnyes (Furiae) were depicted very similarly as hideous snake-haired women.
The other origin is that Medusa was a virgin priestess of Athena, but her incredibly beauty attracted the attentions of the god Poseidon. Eventually Poseidon raped Medusa in Athena's temple. In some versions of this Origin, Medusa actively sought refuge from Poseidon in Athena's temple; in others she was simply performing her duties when he came for her. In either case Athena did nothing to stop the rape, choosing instead to punish Medusa for being violated by turning her into her new hideous form. She was then banished to a desolate island until Perseus slew her.
Medusa is the trope namer to Gorgeous Gorgon. Some of her depictions make her one of the Snake People.
Medusa from Soul Eater is a witch with a pronounced snake theme (including having magical snakes stored in her body and a snake-like "vector arrow" attack). Even though she still looks "human" she still strongly resembles a snake.
Rosario + Vampire has Hitomi Ishigami, a Mad Artist who turns unsuspecting people to stone for her private collection. Her snake hair bites people and the venom slowly petrifies them.
Saint Seiya: The Silver Saints of Perseus, Algol, has a cloth which includes a shield featuring the head of Madusa (just like in mythology). It can turn people into stone whan they look into its eyes. Shiryu tried to defeat Algol with the mirror trick it was believed to have been used against the original Medusa but the Silver Saint, already knowing how she was defeated, didn't fall for it. Shiryu had to pierce his own eyes.
Wonder Woman fought "Medousa". Diana protected herself by blinding herself, and then decapitated Medousa.
In issue four of The Avengers which featured the Silver Age return of Captain America, Cap encounters an alien who turned the other Avengers to stone with a special ray. The alien had been stranded on Earth for thousands of years living in a cave and Cap surmised that the alien's wild hair, made him look like a woman in the shadows and was the basis for the myth about Medusa. Cap got the alien to change the Avengers back and helped him leave Earth and return home. The alien would turn out to belong to the D'Bari, whose planet was later destroyed when the Dark Phoenix caused their sun to go nova.
Clash of the Titans was a bit unusual in that its Medusa was not humanoid. Instead, she was a huge snake with a somewhat humanoid torso on it. The original even added a rattlesnake tail, so she didn't even appear on the screen to scare people. Both versions turn her into an expert archer - with added sociopathy in the remake, where she laughs as she either shoots or petrifies people. In the original film, Medusa was cursed by Aphrodite, for being a willing sexual participant in her temple. Aphrodite then cursed her into her monstrous form out of jealousy. Additionally, in the original film, she was scaly and monstrous all over, while in the remake she was rather beautiful except when she petrified people.
In Dante's Inferno, Dante and his guide Virgil are initially barred from entering Lower Hell at the Gate of Dis in Circle Six. Those at the gate threaten to bring out Medusa to turn Dante to stone; Virgil, not trusting Dante to keep his own eyes closed, covers Dante's eyes with his own hands while they wait for divine aid to come to let them pass through.
Piers Anthony's Xanth book The Source of Magic has a Gorgon with snakes for hair. Any man who looks at her face is turned to stone. She is treated sympathetically since she does not want to do this and is forced to live alone; later she marries the Good Magician Humphrey after he fixes her problem by turning her face invisible.
In Land of the Lost episode "Meddie," a version of Medusa, appears as a beautiful young woman at first, before her hideous true form is revealed.
Robot Wars once had a robot called Medusa 2000; the design spec called for a flail at the back, to look rather like snake hair. Unfortunately, the weapon idea fell through, so all that was left was the name and the picture on the top of the robot, which never was shown clearly on TV.
In one episode of Swamp Thing, Swampy and Dr. Arcane both encounter Medusa in the form of a beautiful woman - that is, she's only beautiful as long as she keeps her sunglasses on. When she takes them off we see glowing eyes and part of a monstrous face. She can't petrify Swamp Thing, as he isn't made of flesh, but she can (somehow) turn him into dry bark. Arcane is a scientist to the core about the whole thing; in one scene she partially petrifies him, and he spends the entire time clinically describing the sensation of his soft tissues being turned to stone.
Since this is a trope about a mythological creature, see the trope description above for the most common versions of the mythology.
Another origin is that Medusa and her sisters were so beautiful that they angered Athena by bragging about being more beautiful than the goddess, in any case, Athena turned them into monsters so hideous men would turn to stone if they looked at them.
A slightly different version of this origin is that they were still beautiful, but they couldn't be looked at without the beholder turning to stone, making their beauty pointless.
So beautiful in fact that anyone who looked at them got hard.
A slightly different version of the second origin is that Medusa was willingly seduced by Poseidon rather than raped.
In some versions, we'll never know if it was consensual. The ancient Greeks (and a number of modern cultures) define rape as having sex with a woman against the wishes of her patron - either her husband, her father, or in this case, Athena. The woman's decision is entirely inconsequential.
In Dungeons & Dragons editions 3 and 3.5, Medusa is an Always Female species with a humanoid body but serpent skin. See page illustration. Petrifying Gaze attack as well as poison bites from the hair snakes come with the package. It is mentioned that Medusas can procreate with any humanoid species, the offspring normally becomes Medusas. There is no official cure for the petrification, but advanced magic can do the job.
In Savage Species, several intelligent monsters including Medusas were made into playable classes: If you wanted to play a Medusa under the standard rules you had to start at level 10 or higher, but with Savage Species you could start as a level 1 immature Medusa who had not yet developed her full potential.
The same expansions also introduced a Feat that allowed Medusas to enable and disable their gaze attack at will, allowing others to see their faces without being turned to stone.
In Dungeons & Dragons fourth edition, Medusas are a species in the usual sense, with both males and females. The female are the classic medusa, pretty much the same as in the previous edition except that she can now un-petrify her victims by applying a drop of her own blood. The males have different powers. Having male medusas with different powers have existed in Dungeons & Dragons before, but this is the first time the concept made it into a core book.
As far as core books go, male Medusas (going by the name of Maedar) appeared in the core Monster Manual of AD&D 2E. Their main power was the ability to cast Stone to Flesh with its touch, thus converting the afflicted back into something edible (after having shattered the statue form).
In the Dungeons and Dragons setting "Scarred Lands", the Medusae species was created by the titan Mormo. In this setting, pretty much everything was created by the Titans, including the Gods. Two centuries ago, the Gods rose up against them in what came to be known as the Titanswar or The Divine War. The Medusae was initially an important force at the titan's side, but they switched side to serve the Gods — particularly the neutral evil goddess Belsameth.
In the Dungeons and Dragons setting Eberron, Medusae have a unique culture largely based around avoiding looking someone in the eyes—they're not immune to the petrifying gaze of other medusae, so its kind of the only choice. They were created by the daelkyr, but broke free when the creatures were sealed away. Oh, and there are explicitly males as well—where do you think all the baby medusae come from?
Magic: The Gathering has its fair share of Gorgons. Most of them have some variety of Deathtouch, which will destroy any creature that gets close to them. One that deserves particular mention is the Xathrid Gorgon which is the only one to actually petrify its enemies.
Kings Quest III To Heir Is Human features a Medusa antagonist in the desert. The hero needs a mirror to defeat her. He also needs to face away from her, or else he's petrified instantly. If he has the mirror and the player types "use mirror" fast enough, the Medusa will see herself and be turned to stone. If he doesn't have it, or doesn't use it quickly enough, she will catch up and force him to look at her.
The AGD Fan Remake added a new wrinkle. She is in a cave instead of the open desert, and there is more than one way to solve the puzzle - the traditional mirror, or a test of character.
Medusas also appear as mooks in many of the other games; particularly the earlier ones.
Medusa shows up in the first God Of War. Her sister was also a boss in the second game.
In Castle Crashers, Medusa appears as a level boss. Snakes jump from her hair and attack the player, and she has an attack that can turn players to stone. When she's defeated, Medusa herself is turned to stone.
Rings Of Medusa does not feature any character with any traits of the mythological Medusa. While "Medusa" is the main villain, she never comes into play herself, and she doesn't have any traits beyond being evil, in a strictly Protagonist-Centered Morality sense of the word.
Dungeons & Dragons games with medusas as monsters include Curse of the Azure Bonds, Gateway to the Savage Frontier, Pool of Radiance, Pools of Darkness, Neverwinter Nights, and Secret of the Silver Blades
The Adventures of Lolo games have a bust of Medusa as an enemy. It paralyzes and kills Lolo if he steps into its line of sight. The only way to get past the busts is to block their line of sight with an egg or Emerald Framer.
Fate/stay night features the actual Medusa (or, more precisely, her Heroic Spirit, i.e. superpowered ghost) as the Servant Rider. While her eyes still turn people into stone, her "snake hair" is explained to be a negative exaggeration of her really long and luxurious hair.
One of the girls in Eerie Cuties has snakes for hair, but is actually a Melusine.
The Order of the Stick has been known to throw in Medusas in the background, so far without ever being part of the plot. There is one standing in line for the ladies' bathroom in the first dungeon the PCs explore.
One of the bonus strips in the Dragon Magazine book depicts Durkon meeting a medusa who is being employed by a dwarf to create cheap building materials. Not that there are many job openings for medusas:
Melissa: I can't even practice my hobbies in peace! I spend two months carving a dog statue, and PETA is all over me.
The Wotch has Scott, who perennially is petrified (and transgendered). On one occasion, this happened when his girlfriend was temporarily changed into a Medusa and looked at him, after he'd been turned into a female elf. They both got better.
One of the Oglaf strips featured a man who survived a Medusa encounter by being distracted her breasts. In the end it is implied that he got more than a Raging Stiffie...
Turns Wonderella to stone in one strip — but she's a Card-Carrying Villain at worst, can be nullified by the simple expedient of wearing sunglasses, and quite apologetically explains that the power to turn people into stone isn't under her control.
The title character from Modest Medusa is a harmless medusa child.
While Medusa herself has not appeared in Wapsi Square, her sister Euryale has, and she gives an amusing re-interpretation of the legend. Medusa's form was always that way; it was not a curse or anything, and the petrification was under conscious control. The deal with Poseidon in Athena's temple was consensual, and Athena put a price on Medusa's head as a result. Then, Medusa fell in love with this Perseus guy, so they conspired to fake her death at his hands and lived the rest of their lives selling statues.
All three gorgons appear in American Dragon Jake Long. Aside from their snake hair, they generally look human, and are both good-looking and vain. In addition to their petrifying gaze (which they must intentionally activate), they're also adept at mind control.
Hurricanes: StavrosGarkos uses the name "Medusa" for some of his business ventures, named his soccer team "Garkos Gorgons" and his big sister once dressed herself as Medusa to trick people into thinking players from a rival team were turned into stone.
The Gorgon sisters in The Smurfs episode "The Smurf Odyssey".