Theo is a Mii from the Wii.
Theo 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 028, however in Wii Music it is 11. His Mii data filename is cpu_mii_028.rcd in Wii Sports, mii_028.rsd in Wii Sports Resort, Wii Fit, and Wii Fit Plus, mii_028.ffsd in Wii Fit U, and is cpu_mii_db11.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 テオ. 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 80-4e-91-1a and his console ID is c2-3d-21-af. His Mii ID tells us he was created on August 27, 2006 at 9:03:36 AM.
According to a September 2020 Nintendo leak about CPU Miis, Theo's nationality is North American.
In this leak, he also has something filled out under his box in "Intellectual Property Comment (2009-04-14)". Translated into English, it reads:
When work on Wii Sports started, the skin color had been brown, but the promotional material remained black. (2009/05/20)
This tells us that he originally had the black skin color (Wii skin color row 2 column 3) and some promotional material was made with him at this point in time, but at some point it was changed to brown (Wii skin color row 2 column 2) and was kept that way in the final game. This had to have happened fairly early, as many other Miis have inconsistencies with their leak icon and final design, but Theo does not.
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 normal. He's ranked 15 in Baseball, 7 in Boxing, and 7 in Tennis. His group IDs are 8, 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 right-handed. He's ranked 67 in Swordplay, 13 in Basketball, 11 in Table Tennis, and 47 in Cycling. His unused Canoe and Debug ranks are both 28, matching his ID value of 028.
In Wii Party, he is one of the Miis to randomly appear as a baby in the Cry Babies minigame. He is also the only male Mii to do so.
Theo unfortunately does not appear in any promo art released.
Names in other languages
Source: Wii Sports Resort