Ice King's crown

The Ice King's crown is the source of the wizard's Ice Powers. The crown is golden, topped with three points and adorned with three red rubies. The crown's jewels are from Magwood, and are what give the object its magic. Also, one of the gems within the crown protects Ice King from the evil brainwashing spells of the Lich.

History
In "Holly Jolly Secrets Part II," it is revealed that the crown was in existence long before the setting of the story. This is confirmed in "Evergreen" as it shows that the Ice King's crown was created by an ice elemental named Urgence Evergreen in an attempt to stop a deadly comet from destroying life on the Earth by giving its first user his deepest wish. Unfortunately, Evergreen's assistant Gunther was forced to try to use the crown and because his wish was to be like his master Evergreen, it transformed him into Gunther's perception of Evergreen. This permanently set the crown's powers, resulting in the same transformation in Simon Petrikov.

Years before the Mushroom War, the magical crown is discovered by an archaeologist named Simon Petrikov. He purchased the crown in Northern Scandinavia from "an old dockworker" as a part of his studies to be an antiquarian of ancient artifacts. He rushed home to his fiancée Betty and put it on in an attempt to make her laugh. While wearing it, Simon experienced visions, which he frantically fought with and shouted at. He also underwent a personality change that he apparently couldn't remember afterward. He realized the crown was doing these things to him and took it off quickly, only to find his fiancée terrified and looking at him with "such contempt." She soon left him. After repeated exposure, Simon Petrikov's body underwent radical changes with subsequent use of the crown. The visions he gained told him that the crown would "protect" Simon "with its frost," though he didn't know what this meant at the time. Simon realized that the crown's effects were becoming permanent, but knew he was "too far gone" to do anything. After the first time he put on the crown he started a series of videos chronicling what had become of him, in hopes that one day someone would help him to free himself from the things the crown was doing to his mind. In the end, the crown turned the calm and intelligent antiquarian into the emotionally confused and mad man known as the Ice King.

In "What Have You Done?," Ice King mentions that he did not steal the crown, although he did make it with stolen magic. It is proved that this is untrue, as stated in "Holly Jolly Secrets." Adam Muto commented Ice King is an unreliable narrator and disassociated from the past of Simon Petrikov, so he presumably does not remember where he got the crown and simply made up the fact that he made it himself. Another possibility is that due to long contact with the crown has caused some of its memories to rub off on him; being totally amnesiac, he may have assumed it was one of his own memories, most likely the memory of when Evergreen stole the ruby eyes from Magwood. In the episode "The Lich," Ice King has one of the gems used to unlock the Enchiridion's true power. It is shown that this gem is the source of Ice King's ice powers in the episode "Crossover" in which Farmworld Finn attempts to use his powers against the Lich, but fails due to the main gem of the crown being in the Enchiridion.

In the episode "Finn the Human," Farmworld Finn puts on the crown, causing him to go insane and have a desire to freeze everything he can, all under the crown's sentient influence. It also causes his hair to grow rapidly, as it did to Ice King, and his hair is used to fly by flapping like wings, similar to the Ice King's beard. It is shown again in this episode that the crown is fully sentient, as it becomes grieved by Simon's death and retaliates by freezing the planet for 400 years.

In the episode "King's Ransom," Ice King was forced to give the crown away as ransom for the kidnapped Gunter, the foxes who stole the crown then gave it to an unknown employer. In a cave the crown floated and turned neon blue, with many polygons and lines almost resembling circuits. The kidnapper then dragged some of the polygons around and the crown started glowing. In a later scene the kidnapper held Gunter up with a device on his head that had a wire running to the crown. The kidnapper then pressed Gunter on the stomach and his eyes glowed and showed Orgalorg's face. The crown stopped glowing and the kidnapper held up their finger and a shining orb of light flew into the crown from their finger and the crown began to glow once more. When the Ice King made it to the cave and begged for Gunter back, the kidnapper was revealed to be Betty, who the Ice King instantly became infatuated with. The Ice King then offered Gunter to her for a hug. When Betty accepted and told the Ice King to close his eyes, she put the crown on the ground and teleported away. When the Ice King put the crown back on, it briefly flashed back in its circuitry form and the Ice King stated, "Feels kinda... different."

In the episode "Broke His Crown," it is revealed that Simon's quote on the crown being a labyrinth was not just allegorical. It appears that whomever wears the crown, not only gets manipulated by its power, but its personality is uploaded into it. Anyone that has ever worn the crown is stored inside the crown's circuitry, while they remain sane and their actual body influenced. Betty had uploaded an A.I. of herself to fix the crown, that would in addition "fix" Simon. She was cured of her madness after Simon reminded of the memories he had of her. His physical mind however is still senile.

Victims of the Crown's Influence

 * Gunther Evergreen (formerly)
 * Santa (formerly)
 * Sveinn (formerly, only wore it once.)
 * Simon Petrikov (current)
 * Farmworld Finn (formerly, alternate timeline)

Abilities

 * For more details on the Ice King's magic, see Ice Powers.

The Ice King's crown is shown to possess immense magical properties, such as granting the wearer control and manipulation over ice and snow. The crown also seems to gives its wearers ability to hear voices of the snow, as seen in "Jake the Dog" where Farmworld Finn mentions the age of ice and whispering snow.

In addition to ice powers, the crown also gives Wizard Eyes so that the wearer may see spirits of the Spirit Realm. This is also stated in "Holly Jolly Secrets Part II" when Simon said he was starting to see strange visions. The crown also seems to have the capability to keep the wearer alive regardless of age. This is suggested in the Adventure Time episode "Simon & Marcy," when it is revealed that Ice King is 1,043 years old.

However, despite the great power that the crown grants, it also has the side effect of changing its wearer's physical appearance. In the case of Simon Petrikov, his skin turned blue, his nose grew long and pointed, his body temperature dropped to around 30 degrees C, his hair and beard grew long and white. Along with physical change, the crown also seems alter the user's mental state. Initially, the crown has an addictive effect that creates a desire to wear the crown. However, the danger of using the crown and the subsequent powers it bestows is evident when Simon becomes more and more "weird" after each successive use, until he becomes the Ice King.

However, the rate at which the crown  reduces its wearer's sanity is proportional to how much resistance is offered to the whispers of power emanating from the crown. In "Holly Jolly Secrets Part II," it is shown that Ice King was using the crown over an extended period of time before the physical changes and control of the crown started. This is likely because Simon Petrikov directly resisted the crown's influence, thus allowing him to retain his sanity for a longer period of time. However, in "Jake the Dog," Farmworld Finn instantly grows paler, and shows rapid hair growth, and immediately shows a decent amount of control over the crown's powers, and turns his voice into a raspy one. Here Farmworld Finn puts the crown on to exact revenge on the Destiny Gang and save his family, making him willingly embrace the powers granted by the crown.

Sentience
"..I see the visions always whether or not I wear the crown. They tell me the secrets... the secrets of the ice and snow... that the power of the crown will save me with its frost."

In "What Have You Done?" the crown is shown to speak and feel regret in the scene where it cries on the Shelf of Penitence. It has a feminine voice. Also, in "Finn the Human", Farmworld Marceline stated that the crown had frozen the world in its grief.

In "Simon & Marcy," Ice King refers to young Marceline as Gunter multiple times, showing another possible effect of wearing the crown: forgetting names, and instead naming people and animals a different name (which in this case is Gunter). This may also be the reason why Ice King's penguins are all (often interchangeably) named Gunter, albeit with several different variations and pronunciations.

The transformed Simon, who was partway Ice King, has been heard on multiple occasions calling Betty his 'princess'. He does so in a frantic state while searching for her, and later when recording a video lamenting that he never found her. This may also be a side-effect of the crown, as opposed to a pre-existing nickname he had for Betty, as there is no evidence of him calling her that prior to him wearing the crown.

The consistent occurrence of these two names is that he has called things in a parent-child relationship Gunter, and those he pursues romantically 'Princess'. As the crown has been indicated to feel emotion, speak and communicate in images, these could be involved in the conveyance of these titles.

Trivia

 * The gender-swapped version of the Ice King's crown is a tiara, as tiaras are worn by female Ooo royalty. Ice Queen referred to it as a tiara when it was knocked off her head in battle in "Fionna and Cake."
 * In "Fionna and Cake," Fionna smacks the tiara off Cake's head, saying "You'll catch her crazy!" Since Ice King wrote this fanfiction, one can speculate that somewhere deep down in his psyche, the Ice King may know that the crown can drive someone mad.
 * Multiple other characters, including Jake, Gunter, and Abracadaniel, have worn the crown without it having any effect on their sanity. This is because the crown already has a living host: Ice King.
 * In the short "The Wand," Ice King's crown has five points for a brief moment after he sacrifices himself to stop the magic wand.
 * Before he reached the state he is currently in as "Ice King," every time Simon wore the crown, his hair and beard would suddenly grow longer, and his nose would grow long and pointed. However, when he removed the crown, his hair, beard and nose would revert back to their normal lengths.Tumblr_ms5qg3kae91rm7i00o6_1280.jpg
 * Simon once used the crown as a weapon by smacking his enemy with it.
 * The crown's only known purpose seems to be to protect whomever wears it. This is implied in "Holly Jolly Secrets Part II," where Simon Petrikov says that the voices he hears while wearing the crown tell him that the crown's power will save him. In "Finn the Human," after Farmworld Simon Petrikov was killed by the mushroom bomb, the crown grieved the loss of its master and retaliated by freezing the entire planet. However, this protection is clearly something of a Faustian bargain, as it comes at the cost of the wearer's sanity. Simon still exists inside of the Ice King (otherwise the crown would have failed to protect him) but is incredibly suppressed, almost to the point of non-existence.
 * In the comics, the Ice King also has another spot for another gem on the inside of his crown. It is currently unknown what the purpose of this gem is.
 * It seems that the crown has a sort of "symbiotic" relation with the host, feeding on its sanity and in exchange giving the control over the ice and snow while protecting the wearer; the physical changes could be a side effect.
 * In "Betty," it is shown that the crown's jewels turn gray when drained of magic.
 * The crown is similar in many ways to the One Ring of Sauron from J.R.R. Tolkien’s Lord of the Rings as it grants the wearer magical powers, protects the wearer from aging, warps the wearer’s personality, and its use is addictive.