He is a creator who has written many novels.
The creator of this work is still unknown.
クリエイター is a loanword often used in modern contexts like digital content creation, whereas 創作者 is a native Japanese term with a slightly more formal or traditional nuance.
Compound of 創作 (そうさく, 'creation') + 者 (しゃ, 'person'). The reading is standard on'yomi.