Oscar is a Mii from the Wii.
Oscar 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, Wii Fit Plus, and Wii Fit U. In most of these games, his internal ID is 027, however in Wii Music it is 05. His Mii data filename is cpu_mii_027.rcd in Wii Sports, mii_027.rsd in Wii Sports Resort, Wii Fit, and Wii Fit Plus, mii_027.ffsd in Wii Fit U, and is cpu_mii_db05.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.
As with every CPU Mii, he has Mingling turned off. His Mii name in his Mii data file is オスカー. 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-81-38 and his console ID is c2-3d-21-af. His Mii ID tells us he was created on August 30, 2006 at 5:21:36 AM.
According to a September 2020 Nintendo leak about CPU Miis, Oscar's nationality is North American.
In the files for Wii Sports, his dominant arm for Baseball (Batting) is right-handed, Baseball (Pitching) is right-handed, and Tennis is right-handed. His unused dominant arm for Boxing is right-handed. His Baseball Pitching style is underhanded. He's ranked 46 in Baseball, 29 in Boxing, and 52 in Tennis. His group IDs are 7, 1, 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 left-handed. He's ranked 38 in Swordplay, 26 in Basketball, 52 in Table Tennis, and 59 in Cycling. His unused Canoe and Debug ranks are both 27, matching his ID value of 027.
Oscar appears in promo art for Wii Music playing the cowbell and Wii Party playing either Flag Fracas or Flag Footrace. The outfit is also used in Splash Bash, but Miis do not run in that minigame. 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, his tie is forest green instead of lime green.
Names in other languages
Source: Wii Sports Resort