WordPress: get author info from post id

I figured it out.

<?php $author_id=$post->post_author; ?>
<img src="https://stackoverflow.com/questions/3188901/<?php the_author_meta("avatar' , $author_id ); ?> " width="140" height="140" class="avatar" alt="<?php echo the_author_meta( 'display_name' , $author_id ); ?>" />
<?php the_author_meta( 'user_nicename' , $author_id ); ?>