#WordPress Get Toplevel Ancestor Page

gistfile1.php

<?php
/**
 * Returns top level ancestor page
 *
 * Usage: $toplevel = get_toplevel_ancestor_page(get_the_ID());
 *
 * @param int|object $post Post ID or post object. Optional, default is the current post from the loop.
 * @return WP_Post|null WP_Post on success or null on failure
 */
function get_toplevel_ancestor_page( $post ) {
	$post = get_post( $post );
	if ( !$post || is_wp_error( $post ) )
		return null;
	if ( $post->post_parent ) {
		$ancestors = get_post_ancestors( $post );
		$root = count ( $ancestors ) - 1;
		$parent = get_post( $ancestors[$root] );
	} else {
		$parent = $post;
	}
	return $parent;
}

Example: get and print top level ancestor's title

<?php
$ancestor = get_toplevel_ancestor_page();
echo get_the_title( $ancestor );
?>