Yuji Naka (中 裕司, Naka Yūji; born September 17, 1965), sometimes credited as YU2, is a Japanese video game designer and programmer. He is the co-creator of the Sonic the Hedgehog series and was the president of Sonic Team at Sega until his departure in 2006.

Naka joined Sega in 1984 and worked on games including Girl's Garden (1985) and Phantasy Star II (1989). He was the lead programmer of the original Sonic games on the Mega Drive in the early 1990s, which greatly increased Sega's market share. After developing Sonic the Hedgehog (1991) in Japan, Naka moved to California to develop Sonic the Hedgehog 2 (1992), Sonic the Hedgehog 3 (1994) and Sonic & Knuckles (1994) with Sega Technical Institute.

Naka returned to Japan to lead development on Sonic Team games including Nights into Dreams (1996), Burning Rangers (1998), Sonic Adventure (1998) and Phantasy Star Online (2000). After Sega left the console market in 2001, Naka remained as an executive officer and oversaw its output for the next five years.

In 2006, Naka left Sega and founded the independent game company Prope. He joined Square Enix to direct the platform game Balan Wonderworld (2021), which reunited him with the Sonic co-creator Naoto Ohshima. Naka said he was removed from the project six months before Balan Wonderworld was released, and it underperformed critically and commercially. He left Square Enix in April 2021. In 2023, Naka was found guilty of insider trading at Square Enix.

Naka was born on September 17, 1965, in Hirakata, Osaka. He learned to program by replicating and debugging video game code printed in magazines. The experience prompted him to study assemblers and practice writing code during his school classes. After graduating, he decided to stay in Osaka rather than enroll in university.

Around 1983, Naka saw that the video game company Sega was looking for programming assistants and applied. Following a brief interview, he began working for Sega in April 1984. His first task was designing maps and checking floppy disks for Lode Runner for the SG-1000; he could not recall if the game was released. His first major project was Girl's Garden (1985), which he and the composer Hiroshi Kawaguchi created as part of their training process. Their boss was impressed and decided to publish the game, and it earned them notice among their peers and Japanese gamers. Naka felt embarrassed about his code, and did not want to release the game. He developed games going with the flow, and did not do task management at all. The pace of game development was 1 game every one or two months, and he was essentially living at the company; he recalled bragging with Yu Suzuki on who worked more overtime.

During the Master System era, Naka wanted to develop games that were not possible on Nintendo's Famicom. Examples of this include the 3D dungeons of Phantasy Star and ports of Space Harrier and OutRun, which ran on powerful arcade hardware. The Mega Drive was introduced suddenly, much like the Master System. It was only around the 32X's release in 1994 that Sega gave Naka information about hardware beforehand. Super Thunder Blade was the first game he programmed for the Mega Drive. He requested that sprite-scaling be implemented in future models of the console. However, he was told that it was not possible at the time. He also requested a 6Mbit cartridge for Phantasy Star II, which was approved. The Mega Drive was Naka's favourite hardware, and he said that he could have kept working on it forever just by making the clock speed faster.

During a visit to the 1988 Amusement Machines Show, Naka was impressed by the ability to move diagonally on slopes in a demonstration of Capcom's game Ghouls 'n Ghosts. Hoping to recreate it, he asked his supervisors at Sega to allow him to port the game to the Mega Drive. Capcom provided him with the source code and ROM data. As he was developing the port, he experimented with aspects such as the speed of the main character to understand how they interacted with the environment. He also altered the slopes and was able to create a functioning 360-degree loop. Sprite-scaling was still a technique that Naka wanted to improve his skill on with a game called Metal Lancer, but it was cancelled halfway through development.