You can access user data directly in the twig template without requesting anything in the controller. The user is accessible like that : app.user.
Now, you can access every property of the user. For example, you can access the username like that : app.user.username.
Warning, if the user is not logged, the app.user is null.
If you want to check if the user is logged, you can use the is_granted twig function. For example, if you want to check if the user has ROLE_ADMIN, you just have to do is_granted("ROLE_ADMIN").
So, in every of your pages you can do :
{% if is_granted("ROLE") %}
Hi {{ app.user.username }}
{% endif %}