get_the_modified_author()

function get_the_modified_author() {
	if ( $last_id = get_post_meta( get_post()->ID, '_edit_last', true) ) {
		$last_user = get_userdata($last_id);

		/**
		 * Filters the display name of the author who last edited the current post.
		 *
		 * @since WP-2.8.0
		 *
		 * @param string $last_user->display_name The author's display name.
		 */
		return apply_filters('the_modified_author', $last_user->display_name);
	}
}