Saburo is a Mii from the Wii.
Saburo originally appeared as one of the 60 CPU Miis to be included with Wii Sports. Since then, he's appeared in Wii Sports, Wii Sports Resort, Wii Party, Wii Music, Wii Fit Plus, Wii Fit U, Super Smash Bros. for Wii U, and Super Smash Bros. Ultimate. In most of these games (aside from Smash Bros.), his internal ID is 000, however in Wii Music it is 41. His Mii data filename is cpu_mii_000.rcd in Wii Sports, mii_000.rsd in Wii Sports Resort and Wii Fit Plus, mii_000.ffsd in Wii Fit U, and is cpu_mii_db41.rsd in Wii Music. Wii Party combines all 100 Mii data files into one larger file named mii_rsd.bin in the same ordering as Wii Sports Resort. His appearances in the Smash Bros. games are limited to prerendered 2D textures, as shown below.
His absence from Wii Fit is explained below.
As with every CPU Mii, he does not have a creator name or birthday, and has Mingling turned off. His Mii name in his Mii data file is さぶろう. In his Wii U/3DS-format Mii data file, he was originally created on a Wii (1).
His Mii data file does not contain any unused data.
In Wii Music, his Mii data file is slightly different. While it's mostly the same as it is in Wii Sports Resort, it now includes a filled out Mii ID and console ID. His Mii ID is 80-4f-90-85 and his console ID is c2-3d-21-af. His Mii ID tells us he was created on August 30, 2006 at 9:42:44 AM.
According to a September 2020 Nintendo leak about CPU Miis, Saburo's nationality is Japanese (Asian).
In the files for Wii Sports, his dominant arm for Baseball (Batting) is right-handed, Baseball (Pitching) is right-handed, and Tennis is left-handed. His unused dominant arm for Boxing is right-handed. His Baseball Pitching style is underhand. He's ranked 14 in Baseball, 6 in Boxing, and 6 in Tennis. His group IDs are 0, 0, and 0.
In the files for Wii Sports Resort, his Wii country ID is 1, like all CPU Miis. His dominant arm for Table Tennis is right-handed. He's ranked 44 in Swordplay, 40 in Basketball, 65 in Table Tennis, and 28 in Cycling. His unused Canoe and Debug ranks are both 0, matching his ID value of 000.
Interestingly, despite Wii Fit containing almost all 60 CPU Miis from Wii Sports, one Mii is absent: Saburo. The reason for his absence is likely a mistake, as he was later re-added to the sequel, Wii Fit Plus.
Saburo's Mii ID is 000 in all games he appears in (with the exception of Wii Music), meaning he is the very first Mii to appear in the files. The second Mii, with a Mii ID of 001, is Hiroshi. Wii Fit does reserve the first 60 Mii data files to the CPU Miis from Wii Sports, however Hiroshi appears twice in the files: once at ID 000 and again at ID 001 where he originally belongs. It is due to this that Saburo's absence from Wii Fit appears to be a mistake.
As mentioned earlier, this was fixed when Wii Fit Plus was released, and Saburo reappears with ID 000.
After defeating the champion of a sport in Wii Sports Resort, the next opponents you face are randomly selected CPU Miis. However, due to a bug in the code, Saburo can not randomly appear as an opponent after the champion. This is because the code for the game randomly selects a Mii from IDs 00 to 99, but that search isn't inclusive of those two values, leaving out both Saburo and Marisa from the selection pool.
Saburo appears in promo art for Wii Music playing the bass drum and Wii Party playing either Space Brawl or Cosmic Capers. He also appears as a flat texture in the background on the Wuhu Island stage in the Super Smash Bros. games. For some images, you may have to open them in a new tab to see the whole render.
Note that in his Wii Music render, some parts look slightly off. His mouth isn't as pointy as it is elsewhere, his mustache is thicker on the outer ends, and his eyes are flatter on the bottom, compared to the oval-ish shape they usually are.
Names in other languages
Source: Wii Sports Resort