A disbeliever, a denier: someone who rejects or disbelieves in God as per Islam (Arabic: الله Allāh) or the tenets of Islam; or more broadly any non-Muslim.
wrongdoer
noun
Someone who does wrong, whether morally, ethically, or in contravention of a law.
How often have the words kafir and wrongdoer occurred in a corpus of books? (source: Google Ngram Viewer )