There was no father.

In the Darth Plagueis novel it’s said that Anakin was created by the Force itself. Darth Plagueis was experimenting with the midiclorians and with the Force to uncover the secret of immortality, but the Force wasn’t willing to be manipulated, so it reacted creating Anakin in Shmi’s womb for the purpose of destroying the Sith who were manipulating the Force, violating the laws of nature. Personally I was never bothered by the virgin birth of Anakin, indeed I always found it a very interesting idea, and to be honest I would have liked much less the idea of Anakin having a father like everyone else. The fact that he was created directly by the Force makes the character much more interesting in my opinion.