Ice King's crown

The Ice King's crown is the source of his Ice Powers. The crown is golden, topped with three points and adorned with three red gems. One of the gems within the crown protects Ice King from the evil brainwashing spells of the Lich.

In "Holly Jolly Secrets Part Two" it is revealed that long before the setting of the story, possibly before the Mushroom War, Ice King purchased the crown in Northern Scandinavia from "an old dockworker" when he was still a human named Simon Petrikov, as a part of his studies to be an antiquarian of ancient artifacts. He rushed home to his fiancée Betty and put it on to try and make her laugh. Upon wearing it, Simon experiences 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, the proto-Ice King developed his Wizard Eyes and his 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. His skin turned blue, his nose grew long and pointed, his body temperature dropped to around 30 C, his hair and beard grew long and white. After so much exposure to the crown he gained power of snow and ice, causing his home town to freeze solid around him unintentionally (which may have been how he created the Ice Kingdom). 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. The crown causes Ice King's emotional confusion and madness, in contrast to Simon's calmness and intelligence.

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 the Christmas special. 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. In the episode "The Lich," Ice King has one of the gems used to unlock the Enchiridion's true power. It's not known if this gem is also the source of the crown's other abilities or its ability to keep the Ice King alive.

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.

Trivia

 * The gender-swapped version of the Ice King's crown is a tiara, as tiaras are worn by female Ooo royalty.
 * In the gender-swapped episode, Fionna smacks the tiara off of Cake's head saying "You'll catch her crazy!" Since Ice King wrote this fanfiction, one can assume that somewhere deep down in his psyche, the Ice King may know that the crown can drive someone mad.
 * In "What Have You Done?" the crown is shown to speak and feel regret in the scene whereShelf-of-Penitence.png it cries on the shelf of penitence. It has a feminine voice. Though this may have only been an effect of the shelf, the crown's sentience was proven in "Finn the Human", when Farmworld Marceline stated that the crown had frozen the world in its grief.
 * Jake has been seen wearing the Ice King's crown in the episode "Thank You," though it had no effect. This is because Jake is already magic according to Adam Muto. Since Cake was able to use the Ice Queen's tiara, it is likely the Ice King is unaware of this fact or he made the fan fiction before "What Have You Done?"
 * In the episode "Paper Pete", when Finn knocks all the books off the shelf one of the books pages has a picture of the Ice King's crown.
 * In the short "Let's Work Together" Ice King's Crown has five points for a brief moment after he sacrifices himself to stop the Magic Wand.
 * 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, but 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. Simon resisted the crown's influence, and Farmworld Finn embraced it.
 * In "Simon and Marcy", Ice King refers to young Marceline as Gunter multiple times, showing another effect of wearing the crown which is forgetting names and instead naming people and animals a different name (which in this case is Gunter). This is also the reason why Ice King's penguins are all named Gunter but with different pronunciations.