Sega CS R&D Dept. No. 1, doing business as RGG Studio (formerly known as Ryu Ga Gotoku Studio), is a Japanese video game developer and a division of Sega. It is known for developing the games in the Like a Dragon series, which the studio is named after since Yakuza 5, and the Super Monkey Ball series.

The studio's origins can be traced back to Sega AM11 in 1998, which was renamed to R&D4 or AM4 in 1999. It was headed by Toshihiro Nagoshi, who joined Sega AM2 in 1989 and has been credited as the creator of the arcade games Daytona USA and Virtua Striker. Although Virtua Striker is attributed to another developer, Satoshi Mifune. Nagoshi requested his own development division during the development of Shenmue.

In 2000, AM4 was re-established as Amusement Vision, where it was best known for Super Monkey Ball and F-Zero GX. Several structural changes occurred in the years that followed. During a reorganization in 2003, the non-sports staff of Smilebit merged with Amusement Vision, and a year later Sega merged with Sammy to form Sega Sammy Holdings. Amusement Vision became New Entertainment R&D Dept. and the first Like a Dragon game was released. Ryū ga Gotoku Kenzan! was the last Like a Dragon game to be developed under the New Entertainment R&D name.

Since Yakuza 3, they were referred to as Sega's CS1 team, all the way up to Yakuza: Dead Souls. The first game to use the RGG logo was Binary Domain in Japan, released in February 2012. Eventually, the RGG Studio's logo became used consistently and the way they brand themselves and give themselves an identity of their own. The current iteration of the logo was introduced during the announcement of the western release of Yakuza Kiwami 2 in 2018. The studio's logo and name have become recognizable internationally for Sega as a whole, although studio leader Masayoshi Yokoyama stresses that it is not a separate company organization but a nickname for a development team within Sega.

Toshihiro Nagoshi joined Sega in 1989 as a designer. As Sega began developing 3D games such as Virtua Racing, he was able to apply his knowledge of film in choosing the right camera angles in three dimensional spaces, something that the other team members had no experience with. Nagoshi became producer, director and chief designer of Daytona USA, which became one of the most successful arcade games of all time. Next he worked on another racing game, Scud Race, which, while successful, did not make as much money as Daytona USA. Nagoshi felt pressure to constantly deliver racing games as he became known for the genre in the company. He developed SpikeOut, which he described as a "personal rebellion" as it was a character based action game where players could play for a long time with just one credit, though profits for arcade operators suffered. Nagoshi requested his own development division during the development of Shenmue.

In what has been called "a brief moment of remarkable creativity", in 2000, Sega restructured its arcade and console development teams into nine semi-autonomous studios headed by the company's top creators. In 2000, Toshihiro Nagoshi was the president of AV (Amusement Vision). Nagoshi chose the name because he was fond of the term "vision", and amusement was the core market of the studio. AV refers to Adult Video in Japan, however Nagoshi thinks with all adult videos being streamed in the future, people will instead think of amusement video when they see AV. Speaking about initial plans for AV, Nagoshi wanted to make original games in addition to sequels. He also was not fond of doing ports of arcade games, believing console and arcade games should be developed separately and in mind for their target market. Of the nine studios that Sega established, AV was the smallest, with about 50 employees.

Nagoshi devised the concept of rolling spheres through mazes based on his desire to create a game that was instantly possible to understand and play, as a contrast to increasingly complex games at Japanese arcades at the time. Another desire for developing the game was to prove that games can be successful without a huge budget, which was a particular complaint from Sega's CEO at the time.

AV developed it initially as an arcade game, Monkey Ball. Monkey Ball was first released in Japanese arcades in June 2001, and then received an upgraded version — Super Monkey Ball — as a GameCube launch game in all regions. After the success of the first Super Monkey Ball, it spawned a direct sequel on the GameCube. Following that, a collaboration with Nintendo happened. AV would develop F-Zero GX in a contracted development, while Nintendo would be responsible for the supervision, production and publishing of their IP. In the end, Nintendo was impressed with the product, considering it a step forward for the F-Zero franchise.