sub-creator
/ˈˌsʌbkrɪˈˌeɪtə/noun
1A secondary or subordinate creator.
2Specifically J. R. R. Tolkien's word for: a person who creates a ‘secondary’ world or worlds. Later also more generally: an author regarded as occupying the position of God in relation to his or her own fictional creation.
Origin
Late 17th century; earliest use found in Samuel Hill (?1649–1716), Church of England clergyman and religious controversialist. From sub- + creator.