Ryo Sakazaki is one of the main protagonists in the Art of Fighting franchise, along with his friend and rival Robert Garcia. He also leads the "Art of Fighting" team in the King of Fighters franchise, represents the "Karate" style in Buriki One, and appears as a secret character in both Fatal Fury Special and Fatal Fury: Wild Ambition. Due to his appearance and techniques, he is often considered a "shoto-clone" of Ryu and Ken from the Street Fighter franchise, and is parodied in that franchise via the joke character Dan Hibiki.
Ryo is the heir to his family's fighting style, known as Kyokugen Karate, and has been given the nickname "The Invincible Dragon" due to his remarkable use and determination of the fighting style. In most games, he is depicted wearing a sleeveless orange gi on top of a black under-shirt and leggings. In some games, he is known as the second "Mr. Karate" (with his father Takuma being the first).
In Art of Fighting and Fatal Fury
In the original Art of Fighting, Ryo teams up with his friend and rival Robert Garcia to scour South Town to find the whereabouts of Ryo's younger sister Yuri. Eventually, they find Yuri has been captured by the crime boss Mr. Big and, upon defeating Mr. Big, they are led to fight against an opponent by the name of "Mr. Karate".
While the original game was left in a cliffhanger, the second Art of Fighting game revealed that the "Mr. Karate" they defeated was Ryo's long-lost father Takuma, who left the family ten years prior and adopted the "Mr. Karate" persona as a henchman of a mysterious crime lord (later revealed to be a young Geese Howard). During the second game, Ryo participates in the first-ever "King of Fighters" tournament.
In Art of Fighting 3, Ryo acts as a supporting character who is hired to find the whereabouts of Robert in the town of Glasshill Valley. He also encounters two challengers who followed him to Glasshill: Kasumi Todoh (daughter of Ryuhaki Todoh, who the duo defeated in the first game, seeking vengeance against Ryo for her father's defeat) and Jin Fu-Ha (former disciple of Eiji Kisaragi from the second game, testing himself against Ryo to find the power to kill his old master).
While not much is known about the cast of Art of Fighting after the events of the first three games, it is known that during the events of the Fatal Fury series (set 20 years later), Ryo leads a dojo (with one of his students, Khushnood Butt, appearing as a playable character in Garou: Mark of the Wolves).
He sports an aged appearance in two games: Fatal Fury: Wild Ambition (as secret opponent "Mr. Karate") and Buriki One (where he participates in the World Grapple Tournament '99 mixed martial arts event), although it is unknown if either of these are canon to the timeline.
In King of Fighters
He always appears in the Art of Fighting team in the King of Fighters franchise, where he is often joined by Robert, Takuma, Yuri, and King. There is often romantic tension between Ryo and King in the series, which Takuma seeks to intensify so there can be a new heir to the family's fighting style. Ryo has appeared in almost every King of Fighters game, which is a rare accomplishment.
One odd biographical note regarding Ryo's KOF appearances, however, has to do with his age and birth date. The Art of Fighting series is set during the 1970s, whereas the King of Fighters series is set in the 1990s and later. Rather than appear twenty years older, Ryo and the other Art of Fighting characters are instead treated as though they were born twenty years later, maintaining their same ages and appearances as in their origin series.