Display posts differently depending on which author wrote it

When you’re in the loop, you can use get_the_author() to get the author’s ‘Public’ name. Alternatively, you can use get_the_author_meta( 'ID' ) in the loop to get the author ID.

So, modifying your psuedo-code:

if ( 2 == get_the_author_meta( 'ID' ) ) {
    echo '<h2>John's Perspective</h2>'
}