$author variable in sidebar? How do I change text per author of post?

All I’m trying to do is get the code in the SIDEBAR to display some text describing the INDIVIDUAL author of each post. How do I do this?

<?php  $author = get_the_author();
if ($author='John Smith')
  echo "John Smith was the author of this post";
elseif ($author='Jane Doe')
  echo "Jane Doe was the author of this post";
else
  echo "Welcome to our site!";
?>

How can I write that code to get it to work inside the sidebar or header?