Voldemort's soul splintered then, killing his physical body and splitting his soul into a new Horcrux. Since he had just murdered Harry's parents in cold blood and attempted to kill a defenseless infant, there was enough justification for the creation of a Horcrux.
Unknown date between 1946 and 1979: While hiding out in a forest in Albania, Tom Riddle murders a local peasant and sends a piece of his soul into Rowena Ravenclaw's diadem (a.k.a. tiara).
Seven is, of course, the most magical number, which is why Voldemort split his soul into seven - each time committing murder to do so. One piece of his soul remained inside him and he chose six objects with a special meaning or connection to him in which to place the other six pieces.
Rowling stated that after his death, Voldemort is forced to exist in the stunted infant-like form that Harry sees in the King's Cross-like limbo after his confrontation with Voldemort in the Forbidden Forest. Rowling also mentioned that, despite his extreme fear of death, he cannot become a ghost.
Voldemort wasn't aware of Harry being a pseudo-horcrux because he didn't plan it, and Harry didn't know either until Voldemort “killed” him, but he actually killed the piece of soul kept in him.
In fact, at the beginning of the series, barely anyone but Dumbledore and Hagrid knew that Voldemort was the charming, successful Tom Marvolo Riddle.
...of the Horcrux, wickedest of magical inventions, we shall not speak nor give direction. This is how taboo the topic of Horcruxes was, not that this stopped Voldemort from endeavouring to have seven pieces of his soul, as seven is usually considered to be the most magical number.
He finds out for sure immediately after Nagini's attack on Arthur Weasley. This night is significant in many ways. While Harry sleeps, he enters Nagini's mind.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
So when Ron said three, it wasn't a mistake. He meant there were three more horcruxes to destroy before being able to destroy the fourth and final piece which was in fact Voldemort himself.
This means that when Riddle made his Diary into a horcrux he split his soul in half and physically removed one half from his body and placed it in the diary. This means that he only had half of his soul left when he made his next horcrux, Marvolo's ring.
If yes, then how did he enter Slytherin without being a pure blood? Yes. Voldemort had a muggle father, and a witch for a mother. Slytherin is not a house exclusive to pure bloods either.
Voldemort is motivated by immortality, superiority, racial cleansing, and more than a bit of self-hatred. Many of these things are shown in earlier books in the series, but become crystallized in the sixth. Tom Riddle has a witch mother and a Muggle father, making him a half-blood wizard.
#1 Lily's Love, The Greatest Protection Charm
Love is the one thing that Voldemort is unable to handle and therefore when Quirrell was touched by Harry, he was burnt by the shield created to protect Harry as a result of Lily's love.
Even after Voldemort returned to full strength in his own body, he was still forced to drink unicorn blood in order to remain alive and strong. To do so, he was able to create a specific potion using unicorn blood and venom from the snake Nagini.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
Her sacrifice gave Harry the power of love, a protection spell sealed with the blood spilled by her death.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
One is that Severus Snape is a master of Occlumency and therefore a difficult target for Voldemort to see through. The second is that Harry himself was not able to block Voldemort, and therefore the overall plan between Snape and Dumbledore was too critical to risk its discovery.
Nothing about Harry being a Horcrux, or Nagini being a Horcrux, or Voldemort having Horcruxes at all. Snape did not know and Dumbledore tried to phrase everything the way it would not specify the kind of magic.
Dumbledore knew that destroying Voldemort's horcruxes was the only way to truly defeat him. He believed that Harry was the one person who was smart, courageous, and perhaps lucky enough to find and eliminate all the horcruxes.
The Secret Horcrux — Harry
Voldemort's soul splintered then, killing his physical body and splitting his soul into a new Horcrux.
Textual evidence: In "Harry Potter and the Order of the Phoenix," Hermione is the first to suggest that Harry's dreams and visions might be connected to Voldemort (OOTP, Chapter 23). This shows her awareness of the link between the two, which could have led her to suspect that Harry was a horcrux.
This theory suggests that each time he created a new Horcrux, that specific Horcrux diminished a part of his soul. Thus, his nose began to sink in, eventually disappearing altogether. Due to his tampering with dark magic, his human appearance evolved into a more snake-like state.