Carnaxus said:
Perhaps the tags need “official” E621 definitions in order to be unaliased. I’ve always understood an original character to be one created by the person making the artwork, and not affiliated with any previously established universe other than the one the original artist is drawing them in.

For example, a picture of Superman in Metropolis done by Stan Lee would be eligible to receive the original_character tag. A picture of Superman in Ponyville done by Stan Lee would still be eligible. However, a picture of Superman in Metropolis done by someone other than Stan Lee would not be eligible for either original_character nor fan_character. A picture of a character invented by the artist, set in Stan Lee’s Metropolis, would receive the fan_character tag, but a picture by the same artist, of the same character, but in the artist’s imagined world would instead receive original_character.

Hopefully that clears it up a bit.

That's a useless definition. If you want Stan's own Superman, search for stan_lee superman. Original_character is too frequently used for the latter case, "I made this character for someone else's world, but the character is mine."