Better author URLs for WordPress. This enables author URLs like /author/firstname-lastname/ or /author/display_name/ instead of the usual /author/user_login/ but comes at a performance cost.

better-author-urls.php

<?php

/**
 * Handle author request to change query string as username
 *
 * This enables author URLs like /author/firstname-lastname/ or /author/display_name/ instead of the usual /author/user_login/
 */
function tc_handle_author_request( $query_vars ) {

    if ( ! empty( $query_vars['author_name'] ) ) {
        $authors = get_users( array( 'who' => 'authors' ) );
		foreach ( $authors as $author ) {
			$matched = false;

			if ( $author->user_firstname && $author->user_lastname ) {
				$name = sprintf( '%s %s', $author->user_firstname, $author->user_lastname );
				if ( in_array( $query_vars['author_name'], array( sanitize_title_with_dashes( $name ), sanitize_key( $name ) ) ) )
					$matched = true;
			} elseif ( $author->display_name ) {
				if ( in_array( $query_vars['author_name'], array( sanitize_title_with_dashes( $author->display_name ), sanitize_key( $author->display_name ) ) ) )
					$matched = true;
			}

			if ( $matched ) {
				$query_vars['author_name'] = $author->user_nicename;
				break;
			}
		}
		
    }
    return $query_vars;
}

add_filter( 'request', 'tc_handle_author_request');

filter-author-posts-url.php

<?php
add_filter( 'author_link', 'tc_override_author_posts_url', 10, 3 );

function tc_override_author_posts_url( $url, $author_id, $user_nicename ) {
    $author = get_userdata( $author_id );
    if ( $author->user_firstname && $author->user_lastname )
        $url = sprintf( '%s/author/%s/', home_url(), sanitize_title_with_dashes( sprintf( '%s %s', $author->user_firstname, $author->user_lastname ) ) );
    elseif ( $author->display_name )
        $url = home_url( '/author/' . sanitize_title_with_dashes( $author->display_name ) . '/' );
    return $url;
}