Brawler is a Mii from the Switch.
Brawler originally appeared as the default Mii for the Mii Brawler fighter in Super Smash Bros. Ultimate. He hasn't appeared in any game since. His Mii data file filename is mii_fighter.bin.
His Mii name in his Mii data file is かくとうF , which translates to "Kakuto F". Kakuto means hand-to-hand combat, and the "F" (possibly standing for "Fighter") is meant to reference how common fighters have their full names said (i.e. people say Bruce Lee and Jackie Chan's full names, rarely ever referring to them just by their first). Thus, Brawler's official name would be Kakuto Fighter. Despite this, the name on the Mii Library is still his title ("Brawler") as this is what he is called in-game and this is information is only known through unused Mii data file info.
His Mii ID is as follows: 7B 37 89 55 90 AC 40 DE AB 49 96 EF E9 BD 39 15
As he is a Smash Bros. character, he has very high quality promo art of his character render, as seen on the left. In Super Smash Bros. Ultimate, he is considered fighter #51.
He is one of few Miis that have a voice actor. In Super Smash Bros. Ultimate, Mii Brawler can choose from 12 different voices, all voiced by Yūji Kishi, Takashi Ōhara, Ryōtarō Okiayu, Michihiko Hagi, Hideo Ishikawa, Kiyoyuki Yanada, Umeka Shōji, Ayumi Fujimura, Makiko Ōmoto, Minami Takayama, and Kimiko Saitō.
Outside of the above Smash Bros. character render, Brawler unfortunately does not appear in much else promo art, aside from the large murals featuring all the characters in the game. There are some promotional screenshots of the Mii Brawler, however, as shown here. For some images, you may have to open them in a new tab to see the whole render.