modder
Not to be confused with moderator.

Someone who mods (or modifies) video games. Though it is more grammatically accurate to use the word modifier, "modder" refers exclusively to the modification of video games.

Notable places to find modders, and the mods they share, are in sites/forums such as "Nexus Mods" and "Steam Workshop".
This character does not exist in the default game, it was created by a modder.