There are loads of Star Wars theories and questions left unanswered from the franchise, including the mystery of Anakin Skywalker's father. Most are inconsequential in the grand scheme of things, while others have greater ramifications for the Star Wars canon. The identity of Anakin Skywalker's father may never be uncovered, but several intriguing candidates exist.
There are hints and insinuations made in the movies about who it could be, but no definitive answer. Some theories are stronger than others, going on the information given by the films themselves. For such a large piece of information in the Skywalker family and in Star Wars in general, it is not a big deal in the actual films. That does mean that there is still room for fans to speculate. With that in mind, here are some of those theories and how likely they are to be the true identity of Anakin Skywalker's father.
Someone From Tatooine
Not a theory that is mentioned in any of the films, but someone from Tatooine being Anakin's father is still a possibility. Either Anakin's mother Shmi forgot about an old acquaintance or chose to lie about who the father is. It's unclear why she would lie, as she said there is no father. Considering just how pivotal this was in understanding Anakin, it seems like an odd choice to go with the chosen one having no father at all.
In Star Wars: Episode I - The Phantom Menace, Qui-Gon was skeptical about Shmi Skywalker's story and believed something else, but maybe the Jedi Master was wrong. Shmi's claim that Anakin's father was no one could have been a mystery to build on during the prequel trilogy, but not impossible. Anything's plausible in the Star Wars universe.
The Force
Qui-Gon seemed to doubt Anakin's parentage details shared by Shmi, indirectly fueling the theory that the boy was a result of the Force. He believed that Anakin was the one who would bring balance to the Force and that he must have been created by it. Consequently, the only way he could have had such a high Midi-chlorian count as if he was created by them in the first place.
If this is indeed the correct answer, it is not known whether it occurred naturally through the Force's search for balance or whether the Midi-chlorians were manipulated by someone or something. All signs point to manipulation, but there is a chance that it was a natural event caused by the Force's eternal journey to finding true balance. This is not the most dramatic answer, but it is the one that makes the most sense. Qui-Gon seemed to be one of the Jedi who had the greatest understanding of the Force, so if he thought this is what happened, then there must be some validity to it.
Darth Sidious
One of the most popular theories is that Darth Sidious is Anakin's father. He could well be his actual biological father, which would go some way to explaining the connection they have, but another interpretation is slightly more complicated. In this theory, the Force is still responsible, just differently. Instead of the Force creating Anakin in a natural event before the prequels Darth Sidious manipulated the Force to create a child inside Shmi. This would go towards Emperor Palpatine's ambition of playing the long game. He didn't rise to power overnight; he waited and planned over decades to get to where he is during the events of the original trilogy.
This would also add even more meaning to the scene between Palpatine and Anakin where he tells the story of Darth Plagueis the wise. Palpatine talks about manipulating the Midi-chlorians to create life. On the surface, it points towards Palpatine trying to bring Anakin to the dark side by implying he will be able to save Padme. It could also be a hint, however, that it was Darth Sidious himself who manipulated the Force to create Anakin Skywalker, subsequently setting him on the path to becoming the great Sith Lord Darth Vader. This is the most likely origin story, as there are multiple hints in the films to support it rather than pure speculation.
Qui-Gon Jinn
As theories go, the idea that Qui-Gon Jinn was Anakin's father is likely the most outlandish. Qui-Gon found Anakin as a boy on Tatooine, freed him from slavery, and set him on the path to becoming a Jedi. It is unlikely that he is Anakin's father as it wouldn't particularly make sense in the movie, but that hasn't stopped fans from speculating about it for years. Without a certain answer, speculation like this is bound to come up. One theory that would back this up as a viable option is that Shmi made up the fatherless birth story to prevent Qui-Gon Jinn from being exiled and ostracized as love was forbidden in the Jedi order.
If the Jedi Council found out, he would have been kicked out. The theory goes then that Shmi decided to lie about it to protect both Qui-Gon and Anakin. In a way, this would parallel Anakin's own love story with Padme, which they kept hidden and ultimately led to Anakin's downfall and transformation into Darth Vader. There is an effective symmetry to this, as is the case for much of Star Wars' canon across the Skywalker Saga. In Anakin's case, it led to the birth of Luke and Leia, and for Shmi and Qui-Gon it led to Anakin. There is a workable way to spin it so that the theory fits the narrative, but it is still a long way from being likely.
Someone/Something Else
There is a possibility that none of the theories listed above are correct and that the right answer to Anakin Skywalker's father is something else entirely. It's possible that this story gets told in a Tales of the Jedi-type project, but that looks unlikely. Star Wars fans traditionally want to know every little detail about every minor character, so not knowing such an important piece of information is hard to swallow. While Darth Sidious is likely the true answer, maybe it is better to view it the way George Lucas intended. A mystery without one set answer, leaning into the spiritualism of the Force, enhancing Anakin as a character in the process instead of bringing it down with a lore-heavy explanation.