ORIGINAL CHARACTER / DO NOT STEAL

About

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Either phrase (or a combination thereof) began as an extremely optimistic appeal to fanartists creating their own versions of characters that their work not be copied or traced by others, which was actually quite common.

Since such a declaration holds little legal weight, and given the nature of the internet re-posting anything of value, it became a sarcastic way of referring to artists trying to exert ridiculous amounts of self important control (see the real life version, Streisand Effect). Adding to the problem is it’s become associated with low quality artists generally creating fan characters by shamelessly copying existing characters with little variation or creativity, generally as self-insert characters, suggesting the idea of anyone copying them is laughable.

Incidentally, it became highly associated with furry fanart and Sonic fanart in particular, culminating in many Sonic fans themselves using the phrase sarcastically to refer to the samey and bloating cast of Sonic games. Likewise, other people may use the phrase to criticize an “official” writer or artists for making a character who is uninspired or identical to another, even within their own work.

Helpful links

TvTropes entry

Oh, Internet!