function wpb_author_info_box( $content ) {
    global $post;

    if ( is_single() && isset( $post->post_author ) ) {
        $display_name = get_the_author_meta( 'display_name', $post->post_author );
        if ( empty( $display_name ) ) {
            $display_name = get_the_author_meta( 'nickname', $post->post_author );
        }

        $user_description = get_the_author_meta( 'user_description', $post->post_author );
        $user_website = get_the_author_meta( 'url', $post->post_author );
        $user_posts = get_author_posts_url( get_the_author_meta( 'ID', $post->post_author ) );

        $author_details = '';

        if ( ! empty( $display_name ) ) {
            $author_details .= '<p class="author_name">About ' . esc_html( $display_name ) . '</p>';
        }

        if ( ! empty( $user_description ) ) {
            $author_details .= '<p class="author_details">' . get_avatar( get_the_author_meta( 'user_email', $post->post_author ), 90 ) . nl2br( esc_html( $user_description ) ) . '</p>';
        }

        $author_details .= '<p class="author_links"><a href="' . esc_url( $user_posts ) . '">View all posts by ' . esc_html( $display_name ) . '</a>';

        if ( ! empty( $user_website ) ) {
            $author_details .= ' | <a href="' . esc_url( $user_website ) . '" target="_blank" rel="nofollow">Website</a>';
        }

        $author_details .= '</p>';

        $content .= '<footer class="author_bio_section">' . $author_details . '</footer>';
    }

    return $content;
}

add_filter( 'the_content', 'wpb_author_info_box' );

// Be cautious with this!
remove_filter( 'pre_user_description', 'wp_filter_kses' );