Well, after reading the entire series twice and having spent a lot of my time with Potterheads, these are the five theories that I actually believe may be true.
- Harry Potter is an immortal.
Now, according to this theory, in her prediction (while a real trance) Professor Trelawney said, and I quote —
"Either must die at the hand of the other for neither can live while the other survives.”
Most interpreted through this that one had to kill the other (as Harry Killed Voldemort). But, this theory interprets the prediction as, One must and can only be killed by the other. This drew a conclusion that Harry defied his death by killing Voldemort.
- Ron is a time travelling Dumbledore.
This theory has been popular since 2004. It states that the chess game in book 1 is the allegory of the series as a whole. Ron plays the knight and the king, just as Dumbledore did in the war. Both are described to be tall, thin with a loose nose, and have auburn hair (for Dumbuldore, it did before it went white). Also, the fact that they have similar qualities, like Bertie Bott's Every Flavored beans.
- Dursleys were under the effects of Horcrux.
This theory stands for poor Dursleys. No doubt, they were so mean to Harry, but a part of the series justifies thee actions, as well. A Tumblr theory draws our attention to the last book of the series, where Ron goes horrible because of a five minutes exposure to the horcrux. This theory suggests that Dursleys were so evil because they were exposed to a horcrux (Harry Potter) for 10 years.
- Deathly Hallows is a symbolic of all books.
This theory of Tumblr states, in the last fight scene of the book Hermoine and Ron are chased by a creature (just like the first book), then attacked by spiders (like second book), then a werewolf appears (the third book), then do the Dementors (like the fourth book), the Order of Phoenix does (fifth book), and finally they got to Snape, the Half Blood Prince (sixth book).
- J.K. Rowling in reality is Rita Skeeter.
The theory argues that, Rita Skeeter was banished from living in magical world after it was discovered that so much of her works were fabricated. So, she then went to live with the Muggles, and fell upon difficult times, so [she] turned to writing in an effort to make a living for herself. This would mean, that the story of Harry Potter is [100] percent true. This all makes sense and fits to reality for crazy Potterheads, as they think no one has that big of an imagination.
Although, the last point may seem a bit stupid to many readers, but as a Potterhead I feel it is a great speculation. These were the theories that made me think and reread the books. I hope they instill the curiosity in you as well.
— Quora user Mrigank Sinha