Muten-Rôshi (in English, the "Invincible Old Master") is a fictional character in the manga Dragon Ball/Dragon Ball Z, and the anime Dragon Ball, Dragon Ball Z, and Dragon Ball GT. He is a human. His name in the English anime adaptation is a phonetic adaptation of that title: Master Roshi.

The name 'Muten-Rôshi' is just a title, the Japanese manga does not give him a real name. However, it is interesting to note that the japanese word "Roshi" translates to "old" (ro) and "teacher" (shi). The character also goes by other titles. Most frequently, he is also known as Kame-Sen'nin (亀仙人 Kame-Sennin, in English, the "Turtle Hermit".) When wishing to act anonymously, Muten-Rôshi has adopted the name Jackie Chun (a parody of martial arts humor master Jackie Chan), although this may or may not be his real name. Muten-Rôshi's first appearance is in chapter/issue #3 of the Dragon Ball manga.

Muten-Rôshi lives on an island with a house built on it, known as Kame House; here, he trains his students. Muten-Rôshi is known as the "Turtle Hermit" due to the heavy turtle shell that he and his students wear on their backs for weight training. At the beginning of Dragon Ball, he is the strongest fighter on Earth, however his power level pales in comparison to any of the Z Fighters later in the series.

Graduates of Muten-Rôshi's training often include the kanji for "Turtle" ("Kame") 亀 on their dogis.

He was Son Goku's and Kuririn's (Krillin) original Martial Arts instructor. He put them through tough training, until they were able to participate in their first Tenka'ichi Budôkai during the original Dragon Ball series. In the tournament Muten-Rôshi had to enter it himself under the Jackie Chun alter ego, in order to make sure that his students did not win it, so that they would still have a challenge and would not become disillusioned. He barely won against Son Goku in the final match.

Muten-Rôshi is at least 300 years old, and provides various stories to explain his longevity and there is some differences between translations. (Immortal Phoenix vs. Foutain of Youth, etc.) Before fighting Piccolo the first time, he does admit however that he is not actually immortal. He has a very dirty mind and is constantly watching young girls on TV in his spare time or looking at dirty magazines. He even bribes the young teen Bulma, to lift her dress for him in exchange for a Dragon Ball, early in the series.

Muten-Rôshi is the inventor of the Kamehameha attack. It took him 50 years to master the attack, while Goku only had to watch Muten-Rôshi perform the attack one time before he could pull off a basic version of it, which he later quickly mastered. Muten-Rôshi also has the ability to increase his body size several fold, transforming himself from a frail looking old man into a larger, more muscular form. (He is the first character in the series to demonstrate a transformation power of any kind.) He does this a few times at various stages in the series, but he is still relatively weak in the form.