Ernie is a Mii from the Switch.
Ernie originally appeared as the default Mii for the Serious Soldier role in Miitopia (Switch, Demo). He later appeared in the full game of Miitopia (Switch). Once the player replaces him with a Mii of their choice, Ernie would never appear again, unless that Mii is deleted. His Mii data file can be found in \cmn\storedata\npc_default_mii.sarc and is named Castle00_Soldier00.charinfo.
His Mii name in his Mii data file is マジメへいしk, which translates to "seriously k". His height is set to 127 (maximum) and his build is set to 127 (maximum). His Mii ID is as follows: 02 0A AD AC 4B 46 44 1E 94 95 C1 BA 04 FC 02 F7
His Mii data file does not contain any unused Mii data.
Ernie's role in Miitopia (the Serious Soldier) is described as so:
He seems to bear resemblance to Leonel, as it seems a handful of the Miitopia Switch default Miis were based around Wii U/3DS CPU Miis, but there are still visible differences between Ernie and Leonel.
The names of the default Miis in Miitopia Switch often vary drastically depending on region. Ernie's name on the Mii Library is going off of the US English version, for consistency. A chart containing all of Ernie's names is located at the bottom of this page.
Below is a screenshot of Ernie in-game as his role in Miitopia.
Ernie appears in promo art for Miitopia (Switch), on the face of the Cerberus monster, along with Clara (Switch) and Rudy, as well as the Robo-"Traveler" and Woof-o'-the-Wisp. Note that these monsters only take the faces of different roles, while Ernie is the Serious Soldier. For some images, you may have to open them in a new tab to see the whole render.
This Mii originally appeared on the Switch!
Here's how to recreate them on the Switch:
Names in other languages
Source: Miitopia (Switch, Demo)