Unicorns are one of the most beloved magical creatures in the world - even outside of the wizarding world of Harry Potter. These horned horse-like creatures are the embodiment of all that is pure and graceful and good in the world, and this is a symbolism that carries over into the wizarding franchise. In Harry Potter, unicorns first appear when Voldemort is killing them to survive (a truly heinous crime), but this isn't the only way that the magic of a unicorn can be harnessed.
A much less horrifying way to tap into the powers of the unicorn is to use their hair as an ingredient, or as the core of a wand. As all wands have specific properties dependent on their cores (and their wood, length, shape, and flexibility), a unicorn hair core will create a very unique wand - and is one of the most popular wand cores in the series.
Unicorns Don't Have To Give Their Hair For Wandmaking
It is mentioned in the series that some magical creatures actively donate their hair/feathers for wandmaking (like Fawkes the Phoenix), and it is implied that others are difficult to get because of the rarity or wildness of the animals (like Thestral hair). However, unicorn hair isn't difficult to find, and doesn't have to be given by the animal - as Hagrid tells Harry, unicorns shed, and he often finds their hairs in the bushes of the forest. This may make it one of the easiest core materials to get hold of for wandmaking.
The Second Most Popular Wand Core In Harry Potter
While many different wand cores are mentioned in the series, most characters have either a Dragon Heartstring or Unicorn Hair wand core (where their wand cores are stated). Around fourteen Dragon Heartstring wands are mentioned in the series (including Hermione's), but ten characters are described as having unicorn hair cores. This list includes Ron Weasley, Cedric Diggory, and Remus Lupin.
The Unicorn Wand That Rejected Harry Had A Link To Voldemort
When Harry was first choosing his wand at Ollivanders (or, more accurately, when his wand was choosing him!), one of those that did not work had a unicorn core. It was a yew wand, eight and three quarter inches long, and it was a definite 'no' for Harry.
As fans know, he was destined to pick up the wand with a core that is the brother of Voldemort's wand. However, had this unicorn hair wand been picked, there would still have been a connection - in the wand wood. Tom Riddle's wand was also yew, but with the Phoenix feather core.
Unicorn Hair Wands Are The Most Consistent...
According to Pottermore, "unicorn hair generally produces the most consistent magic, and is least subject to fluctuations and blockages". The reason for this consistency isn't given, but presumably, it has some kind of connection to the calm and peaceful nature of the unicorn itself - and the purity that it represents.
... And The Most Loyal
As revealed by the complicated shifting ownership of the Elder Wand between Dumbledore, Snape, Draco, Voldemort, and Harry, wands have the ability to choose to serve a different wizard - but not all are likely to. Pottermore also describes wands with a unicorn hair core as loyal - and as wands that are not swayed by the power or skill of a witch or wizard. Like the consistency of the magic, this is likely connected to the unicorn itself, and the loyalty that this animal is known for in legend.
It Is Almost Impossible To Turn A Unicorn Wand Dark...
Because of the purity and inherent goodness of the unicorn itself, a unicorn hair core wand is one that will not often be found in the hands of Dark witches and wizards. These wands are the hardest to turn to Dark magic, and while a powerful wizard may be able to do it, it is far more likely that a witch or wizard with a unicorn hair wand would struggle to perform Dark spells or Forbidden curses.
...Which May Have Hinted At Draco's True Nature
Interestingly, Draco Malfoy's wand was made of hawthorn wood, with a unicorn hair core - which may have been a hint at his true nature. Although Draco appears to be a Dark wizard in the making, as the series continues, it becomes increasingly clear that really, he's just a spoiled little boy going along with what he has always been told.
He struggles to really hurt people, even though he is a bit of a schoolyard bully, and can't bring himself to kill Dumbledore. In the final books, he is frightened, in over his head, and even turns away from the Death Eaters. Perhaps his unicorn hair core was a hint that he wasn't evil after all.
Unicorn Hair Costs Ten Galleons
The money, and the cost of goods, in the wizarding world of Harry Potter is well-known to be inconsistent, at best... but be that as it may, it is stated in the series that a strand of unicorn hair costs ten galleons. This makes little sense, as wands cost seven galleons. However, it's possible that the reference to the cost of the hair (made by the greedy Horace Slughorn) was inflated due to his inebriation, or that wandmakers are able to get their unicorn hairs at some kind of a discount.
Unicorn Hair May 'Die' Inside A Wand
In the series, fans learn that wands can be broken, but for a unicorn hair wand, it is also possible for the wand to 'die' thanks to mistreatment. If they are 'mishandled' (according to Pottermore), they will become 'melancholy' and eventually die and stop working. What kind of 'mistreatment' would lead to this is left up to the imagination, but it is likely the kind of Dark magic that the unicorn wand would reject.
Unicorn Hair Is One Of The 'Supreme Cores'
According to Ollivander, there are three types of wand cores that are the best: Unicorn Hair, Dragon Heartstring, and Phoenix Feather. (It's no coincidence that these are the three most common types of wand core in the series, either, or that Harry, Ron, and Hermione have one of each.) Referred to as the 'supreme cores', these are the best core materials, and are all that Ollivander will now use in his wandmaking.