Who is Man vs Himself in Of Mice and Men?

George goes through a mental struggle with himself over what to do when Curley and the ranch hands set out to kill Lennie. He eventually decides to kill Lennie out of love and mercy. He doesn't want Lennie's last moments filled with fright and anger and Horror. George instead speaks to him of their now hopeless dream and fills Lennie's last moments with happiness before shooting him so the angry ranch hands won't.