This is by far my favorite character. Happosai is the ultimate master of Anything-Goes-Martial-Arts and uses a long-stemmed pipe as his favorite weapon. He is over 100 years old and about a foot and a half tall, a thief, a glutton and everyone hates him. He is also a master of perversion. Happasai trained Genma and Soun in the Anything-Goes-Martial-Arts. One day, though, Soun and Genma finally got away from Happosai's control. While Happosai was passed out drunk from wine that they brought to him, Soun and Genma took Happosai, trapped him inside a box, threw the box in a cave, caved-in the entrance, and rolled a boulder over it. Thinking they were finally free of Happosai, Soun and Genma left to continue their lives. After many years, though, Happosai managed to escape from this prison and make his way to the Tendo dojo. Fearing that Happosai was out for revenge, Soun and Genma immediately groveled before his feet. Happosai, though, was only looking to "train" the next heir to the school of Anything-Goes-Martial-Arts - namely, Ranma.

Knowing full well about the "training" of Happosai, and also of his incredibly lecherous nature, Ranma refused to follow him. Since then, Happosai has made several attempts to defeat Ranma in order to train him, and at the same time, moved into the dojo and made a nuisance of himself in his panty-stealing and perverse behavior toward any of the females in the household and in the neighborhood in general. He daily raids Akane's and Nabiki's high school girl's locker room to steal all the girl's underwear. He is usually introduced into an episode being chased by an enraged horde of girls and yelling "What a haul! What a haul!"

He derives his superhuman martial arts strength (his ki) from foundling girl's lingerie and the young girls themselves. As a result, he is constantly thowing cold water on Ranma-kun then trying to grope Ranma-chan. When deprived of his foundling he rapidly weakens and is immediately attacked by Genma and Soun.

When Ranma, Genma or Soun try his patience with their refusal to do what he wants, he grows extraordinarily vindictive. He goes on rampages, ordering expensive takeout food to the Tendos which they then have to pay for, putting tacks in their shoes, poking holes in the rice paper panels of the house. He's incidious.