Training with his father at the mysterious Jusenkyou training ground in China, he was thrown into a spring called Nyanniichuan, where a young girl drowned 1500 years ago. He emerged as a young girl, according with the spring's curse. When splashed with hot water, he changes back to a boy, but when splashed with cold to room temperature water, he turns into a girl again.
While training Ranma at the remote Chinese training ground Jusenkyou, Ranma kicked him into Shonmaoniichuan where a panda drowned 2000 years ago. Genma emerged as a panda, and as the guide explained the spring's curse, still went on to whack Ranma into Nyanniichuan.
Unlike Ranma, he doesn't have much trouble with his curse, and becomes quite accustomed to living as a panda (comporting himself with human dignity even as he sips tea and plays shogi with Souun). Since he can't speak as a panda, he uses wooden signs to communicate.
Despite their constant bickering and denials, Akane and Ranma grow to like each other (and feel jealous when the other appears more interested in another suitor), but neither can admit it.
Akane is comically inept at traditional feminine pursuits like cooking, sewing, and tea ceremony. She also swims like a hammer, being utterly incapable of staying afloat.
Souun and Genma trained together as Happousai's students before starting their own martial arts schools. Now the fathers try to force Akane and Ranma to bond against their will, which rarely does any good. Souun is furious whenever Ranma turns out to have yet another fiancée, or when Ranma seems to prefer one of them to Akane.
To avenge the grudge, he went to China after Ranma, eventually blundering his way to a desolate mountain range, where a pony-tailed girl chasing a panda knocked him off a cliff and into Heitouenniichuan, where a black pig drowned 1200 years ago. A panda rescued the little black pig... only to deliver him to the Chinese guide for dinner. Fortunately, the guide dropped him into a wok of boiling water.
Ryouga blames Ranma for his condition, and his anger multiplies when he finds out that Ranma is really directly responsible for it. When this comes out, Ranma remorsefully swears not to reveal Ryouga's secret.
Akane adopts Ryouga the pig as her pet "P-chan". Ryouga falls deeply in love with her. However, he feels certain that no one could love him as a human with his curse. Akane is unaware that the pet pig she sleeps with is Ryouga, despite several close calls, and is angry whenever Ranma abuses her piggy.
In addition to a complete inability to follow directions, Ryouga is fooled even by Ranma's most ridiculous disguises. Extremely strong, he often shatters rocks and walls in his anxiety.
As class president, he ruled that anyone who would date Akane must first defeat her. At the start of the series, Akane defeats their attempts every morning. In the meantime, he falls in love with the pony-tailed girl who mysteriously takes Ranma's place during a fight and defeats him. After Ranma soundly defeats him, though he will never accept defeat, the other students accept Ranma and Akane's betrothal.
Hating Ranma for being too close to both Akane and the pony-tailed girl, he agonizes over which girl he loves more (which his classmate Nabiki capitalizes on).
However, not only is Akane in the way, but also a strong pony-tailed girl who has the audacity to use her Ranma's name!
In the manga, the students force him to reveal that although he doesn't remember where that coconut with the exemption slip is, he tattooed directions to it on the shaved head of his long lost son Tatewaki, who he left behind 3 years ago. He makes crazy rules to inconvenience his students, especially Ranma, who thwarts his discipline.
Years later, he escapes. He moves into the Tendou doujou to train his successor, where Genma gives him Ranma to train.
A 110% pervert, he constantly goes around lifting skirts, stealing women's underwear for his extensive collection, and committing frottage. His perversions are the source of his strength; without touching young female bodies or underwear, he loses his power. Ranma and Akane are his favorite targets.
Ukyou's father told Genma that Ukyou said she wants to be Ranma's wife. Genma said Ranma already has a fiancée. Ukyou's father said too bad, he was thinking of giving them the yatai for a dowry. Genma said we'll take her.
In this quandary, he made Ranma decide; he asked Ranma which he liked better, okonomiyaki or Ukyou. Unaware of Ukyou's wish or even that Ukyou is a girl, Ranma chose okonomiyaki, so Genma and Ranma ran off with the yatai and leave Ukyou behind. Shamed and ridiculed by her peers, Ukyou decided she wouldn't like boys forever, dressed and lived as one, and devoted herself to okonomiyaki style martial arts.
Years later, when Ranma discovers her actual gender and Ukyou discovers that Ranma does not get along with his other fiance;e, they reconcile and she becomes enamored of him. Ranma generally treats Ukyou only like an old friend. She runs the Utchan okonomiyaki shop in town.
Ruthless with her rivals, she tries to make Akane forget everything about Ranma by washing her hair with her special formula 110 shampoo.
Crushed when Ranma reveals his secret to her, she returns to her village and renews her training at Jusenkyou with her grandmother, who knocks her into Maoniichuan, where a cat drowned 1800 years ago. Assured that Ranma is really a man, she returns to Japan and tries to get Ranma to fall in love with her, working at her great-grandmother's Chinese restaurant and making deliveries on her bicycle.
nii hao hello shai shen bye bye shei shei thank you wuo ai ni I love you wuoda airen dear husband
She and her granddaughter Shampoo run the Neko Hanten restaurant.
(Only a background character, but he has a big part in the PC Engine CD-ROM action game as the boss of the final stage.)
He shows up in Japan looking for Shampoo, even though he always fails to defeat her in a fight, but Cologne tells him Shampoo is going to marry Ranma. So he challenges this new rival for Shampoo's affections to a man-to-man fight (a troublesome point for Ranma).
When Ranma defeats him, he returns to China and seeks training at Jusenkyou, where he walks into Yaazuniichuan, a spring where a wild duckling drowned 1300 years ago (if there's anywhere in the world a duck could drown, it's there). He returns to Japan with a supply of Yaazuniichuan water to turn Ranma into a duck, too, but (of course) fails.
Moose hates Ranma, and would dearly like to do away with Shampoo's "husband".
Skilled at camouflage, Tsubasa wears bizarre disguises like mailboxes, vending machines, umbrella costumes...
Twenty years ago, a starving Souun and Genma, after losing in a martial arts dinner contest and being presented with a monstrous bill, promised one of their daughters to marry into the Chardin family.
Happousai baptised Tarou in Niuhoomanmaorenniichuan, where a yeti riding a bull carrying a crane and an eel drowned 2500 years ago. But it's not turning into a bizarre monster that upsets Tarou... Happousai cursed him with something even worse-- he baptised him with the humiliating name "Pantyhose Tarou", and by his customs, only Happousai can change his name.
When she was a sickly child, Happousai trained her in what she thought was "best gymnastics". In fact, he taught her the Happou-goen-satsu "ki" absorbtion technique to take out the opposition to his panty raids. When she absorbs "ki", her body grows and she takes on the personality of a soldier.
By infiltrated the Tendou doujou and pretending to be Ranma, he hopes to find the technique the Yamasen-ken pairs with, the Umisen-ken.