When read in the Japanese fashion the name "kumonryu" translates as "dragon of nine markings." This is a type of koi fish which comes from the karasu, or black stock, but often appears to be wearing the black coloration like a garment.
Ryu has short dark hair held back by a white headband. He dresses in a quasi-military style, with a black tank top, utility belt, black gloves, fatigue pants, and combat boots. He began dressing like this after setting out on his journey to find the Umi-Sen Ken as a young boy. Prior to this he wore a patchwork gi due to poverty.
Ryu Kumon is a driven, manly, and quite ruthless, martial artist, and was willing to go to extremes in order to restore his family's dojo, including pretending to be Ranma, attempting to rip the latter's heart out when he was distracted by his mother, threatening to expose the latter if he interfered, and briefly considered torturing Nodoka for information, but couldn't go through with it.
The deaths of his parents, and his harsh lonely life have turned him fierce, cold, militaristic, and independent, seemingly preferring killing to stunning strikes (against the bear and during his initial confrontation with Ranma). Ryoga, and Konatsu, are the only characters in the series that are at least as miserable as himself.
However, his word is his bond, he has a strong chivalrous streak and saved the life of Nodoka without a second thought when he thought that she was an endangered bystander; and he was very touched by, and grateful for, her motherly love, and reevaluated his life after learning the truth of his school. So, much like them, he seemed very positively affected from being treated with consideration.
Unlike most other young male fighters in the series, he is not shy with attractive young women, and seems quite confident in his ability to charm them. He also mostly lacks the usual goofy quirks, and seems unused to magic oddities.
Ryu is a wandering martial artist and expert in the Yama-Sen Ken. When he was a young boy, he and his father were a very poor family that owned the shoddy Kumon Dojo. One day Ryu's father had an encounter with Genma Saotome. After Genma found out about the Kumons' financial problems, he gave Ryu's father a scroll containing the techniques of the deadly secret art of the Yama-Sen Ken. This led Ryu's father to believe he could use the techniques to restore his dojo, but when he practiced its attacks indoors he ended up destroying the building, causing it to fall onto and him and inflict mortal injuries. With his last moments of life, he gave Ryu the scroll and told him to find the scroll containing the companion Umi-Sen Ken. Since then Ryu has traveled alone without any family or friends, which led to his harsh and untrusting nature.
Ten years later, he comes across Genma's wife Nodoka, when saving her from a rampaging bear, she tells him that he is her long lost son, Ranma, since the scroll he is carrying has Ranma's name written on it. While somewhat surprised by his coincidental good fortune in encountering the wife of Genma, Ryu immediately takes the opportunity to play along, in order to find the Umi-Sen Ken scroll, and takes up residence within her house. Ranma discovers that Ryu is misleading his mother, and after being beaten and threatened to be exposed if he interfered, decides to learn the deadly Umi-Sen Ken from his father in order to counter Ryu's Yama-Sen Ken. Once Ranma mastered the Umi-Sen Ken, he finally managed to defeat Ryu after a harsh and difficult battle.
After the fight, Genma informed Ryu that the Umi-Sen Ken and Yama-Sen Ken were created for burglary and robbery, respectively. He gave the scroll to Ryu's father so that he could steal enough money to be able to afford to rebuild his dojo. After learning this, and being told that even this represented a way to live, while all he was using them for was empty destruction, Ryu was saddened with regret over having wasted years in an empty pursuit. He sealed the scroll in a hole covered with dirt together with the Umi-Sen Ken and (temporarily) Genma himself, possibly forswearing to personally use them as well. Although Ryu knows about Ranma's dual identity, he refrained from revealing this to Nodoka and used his parting words to tell her that Ranma may be closer than she thinks in order to provide some comfort. He remains fond of Nodoka, and seemingly turned into a nicer person from the combination of her motherly kindness and the conclusive cathartic revelation.
Ryu was able to teach himself the Yama-Sen Ken from the scroll that Genma had given his father. He had become a master of the style after years of solitary wandering while searching for scroll containing the Umi-Sen Ken. Thanks to his unorthodox and ruthless fighting style, Ryu was one of Ranma's most dangerous adversaries and defeated him twice. However after learning the Umi-Sen Ken Ranma challenged Ryu to a climactic duel where he would either gain the Umi-Sen Ken if he won or seal away the Yama-Sen Ken if he lost. Despite Ryu's best efforts, he fell to theUmi-Sen Ken's ultimate technique and upheld his end of the bargain.
Despite Ryu being a one time only character in the manga, he did make an appearance in the video game Ranma ½: Battle Renaissance, in which he was voiced by Mitsuru Miyamoto. There was a planned dubbed version where he was to be voiced by Matt Smith, but it was never released for unknown reasons.