Avada Kedavra - Used 8 times. It is common to see this curse used by the Death Eaters and by “He Who Must Not Be Named.” This spell is based on the Aramaic, meaning "disappear like this word."
Throughout the Harry Potter series, the titular hero never used the Killing Curse for several reasons. Avada Kedavra was Lord Voldemort's signature spell. In fact, the Dark Lord directly killed multiple notable figures, including Harry's parents Lily and James Potter, with the Killing Curse.
Harry makes use of two of the Unforgivable Curses in the books.
And yet in seven books and eight movies, no one but the title character himself has ever walked away from The Killing Curse (one of three Unforgivable Curses that causes instantaneous death), and Harry managed to do it twice.
Lily's Protection In Voldemort's Blood Saved Harry
However, Lily's protection simply took on a new form when he created a body from Harry's blood. As Dumbledore explained, "His body keeps her sacrifice alive, and while that enchantment survives, so do you."
And while many fan-favorite characters have fallen victim to the Killing Curse, one surprising figure working at Hogwarts School of Witchcraft and Wizardry may possess limited immunity from the spell's full, lethal effects: Rubeus Hagrid.
Avada Kedavra, also known as the Killing Curse, kills a person instantaneously and without injury. There is no countercurse for it, and only one person, Harry Potter, has ever survived it.
Albus Dumbledore
Voldemort sent young Draco Malfoy to kill Dumbledore, and the great wizard knew that the young wizard had no choice. To save Draco's soul, he signaled Severus Snape to kill him, which Snape did instantly. It was one of the most heartbreaking deaths Harry faced.
The Killing Curse was created in the early Middle Ages by Dark witches and wizards. Primarily, the curse was used to quickly slay opponents during a duel. In 1707, the Wizards' Council was restructured into the Ministry of Magic, which allowed for more strict restrictions on certain types of magic.
Only love itself, the strongest magic of all, can block the Killing Curse. Lord Voldemort cast this spell constantly in his lifetime, and it's the spell that killed Harry's parents in particular.
Crucio (Cruciatus Curse) - Used 5 times.
Another of the Unforgivable Curses. Cruciatus is used to do terrible harm to an opponent, basically to torture them.
Cruciatus Curse ('Crucio')
Harry tried to use this spell himself. The first time was against Bellatrix after she had killed Sirius. His attempt was unsuccessful because, as Bellatrix mockingly explained: 'You need to really want to cause pain – to enjoy it – righteous anger won't hurt me for long…'
None of the good guys dare use the Killing Curse throughout the events of the movies and books, no matter how high the stakes and how difficult things are. But Ron Weasley is the exception, giving it a go in the Deathly Hallows: Part 2 movie when himself and Hermione look destined to die via Nagini.
Expelliarmus did not beat Avada Kedavra.
Voldemort's wand (the elder wand) recognized its true master (that was Harry) and refused to attack it. In a way Voldemort killed himself as his own spell backfired on him.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, the wizard never cast, or even considered casting, that particular spell. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
Professor Snape taught Harry the spell
It was during Professor Lockhart's short-lived Duelling Club that Harry learned the spell that would define him. Not from Lockhart (of course) but from Snape.
Why is Avada Kedavra considered unblockable in Harry Potter? It was so because the curse was one of the unforgivable curses and there are no ways of stopping it coming to you.
To Be Confronted By A Dementor
The confrontation with a Dementor on the Hogwarts Express made Harry realize that this creature was his deepest fear in a corporeal form.
Horace Slughorn really exemplified the Slytherin skill for self-preservation. He didn't seem to do anything that wouldn't benefit him, so you'd be forgiven for thinking he might not wish to stick around and risk his life. But he did – and faced Voldemort himself.
Narcissa Malfoy's Very Dangerous Lie
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.
Narcissa's greatest moment, however, was when she chose to betray Voldemort in Harry Potter and the Deathly Hallows. Not knowing whether Draco was alive or dead, Narcissa chose to lie to the Dark Lord rather than risk losing her son.
Its incantation is Avada Kedavra. The only known counter-spell is sacrificial protection, which uses the magic of love.