Not to be confused with the creator of the same name.
Unknown creator is the term given to a creator whose identity isn't known.
Reasons for a creator not being identifiable are numerous. Most commonly, it happens when a creator creates a character or stage and neglects to include an author field in the .def file, or does not include a readme file that states their identity. Another common reason is when a creator edits another creation, but does not modify the author field to denote that they were the one to have edited it; this can be seen with characters erroneously credited to Elecbyte, often as a result of either editing or basing their character off of Kung Fu Man.
Theoretically, an unknown creator could be identified by finding the original source website of the creation in question, and then seeing who it belonged to. However, this can be quite difficult in practice, especially with older characters whose original source sites has since been shut down and are now only available through warehouse sites.