A Father is something a man becomes by participating in ( or at least going through the motion of ) a Biological act! In fact you can even become one posthumously.

Whereas becoming a Daddy is a labour of love.

A Daddy/Dad is a loving parent.

The guy who picks you up and comforts you when you need him and many a time that you don't but he just likes to.

Who confronts and corrects you when needed.

Whose fingers you tighten your palms around when you're in a strange place. Whose legs you cling to as he investigates the monster who you were sure lurked under your bed.