Anakin is, like Jesus of Christian belief, a virgin birth. His mother Shmi was never with a man when she conceived Anakin. It is implied that Darth Plagueis, master of Darth Sidious, has the ability to command the Force to spontaneously create life--like Anakin--so there is the theory that Plagueis is, in many ways, Anakin's father, but not by blood relation, if indeed it is true at all.