This copyright tag is used to indicate the presence of at least one original character in an image.
Also note borrowed character is used when secondary artist draws an OC created by an earlier one. This doesn't apply to other artists drawing a mainstream franchise though, just the adoption of non-mainstream chars.
In some cases where the artist who creates a franchise draws art of the character, both 'original' and series name would be appropriate tags to coexist.
If an original character's name is known, please create a green character tag for them.
In the case of it being a common name, if there is no known series name to put in parenthesis, instead use the artist/creator of the OC's name in parenthesis.
One should only use deprecated tags like original character or oc as a green character tag if you do not know the name of an original character. This tag is useful only to indicate unknown or un-named OCs. If you think they probably do have a name character request is a better idea.
You'll find stuff like Danbooru and Gelbooru solely use the 'original' copyright tag and don't have "OC" or "original charater" green tags too as that is superfluous. It does not add any extra information except perhaps to indicate the presence of an un-named OC who is accompanying a named one in an image.
The following tags are aliased to this tag:
/o
(learn more).
