Martin is a Mii from the Wii.
You may get them confused with martin (WarioWare)!
Martin (Wii) 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 043, however in Wii Music it is 13. His Mii data filename is cpu_mii_043.rcd in Wii Sports, mii_043.rsd in Wii Sports Resort, Wii Fit, and Wii Fit Plus, mii_043.ffsd in Wii Fit U, and is cpu_mii_db13.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 マルティン. 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-81-36 and his console ID is c2-3d-21-af. His Mii ID tells us he was created on August 27, 2006 at 4:32:24 AM.
According to a September 2020 Nintendo leak about CPU Miis, Martin (Wii)'s nationality is German.
In the files for Wii Sports, his dominant arm for Baseball (Batting) is left-handed, Baseball (Pitching) is left-handed, and Tennis is right-handed. His unused dominant arm for Boxing is left-handed. His Baseball Pitching style is underhanded. He's ranked 48 in Baseball, 33 in Boxing, and 49 in Tennis. His group IDs are 3, 2, 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 94 in Swordplay, 88 in Basketball, 62 in Table Tennis, and 9 in Cycling. His unused Canoe and Debug ranks are both 43, matching his ID value of 043.
Martin (Wii) appears in promo art for Wii Music playing the NES horn.
Names in other languages
Source: Wii Sports Resort