PHP

wordpress get post author link

<a href="<?php echo esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ); ?>" 
  title="<?php echo esc_attr( get_the_author() ); ?>">
  <?php the_author(); ?>
</a>

wp get post author link

<?php $author_id=$post->post_author; ?>
<img src="<?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 ); ?> 

wp get post author id

$post_id = 257;
$author_id = get_post_field( 'post_author', $post_id );