'Adversary' in the Bible

David answered, “Sons of Zeruiah, do we agree on anything? Have you become my adversary today? Should any man be killed in Israel today? Am I not aware that today I’m king over Israel?”

And the anger of Jehovah addeth to burn against Israel, and an adversary moveth David about them, saying, 'Go, number Israel and Judah.'

And Gad cometh in unto David, and declareth to him, and saith to him, 'Do seven years of famine come in to thee in thy land? or three months art thou fleeing before thine adversary -- and he pursuing thee? or are three days' pestilence in thy land? now, know and see what word I take back to Him sending me.'