Simon Petrikov, more commonly called the Ice King, is a fictional character in the Adventure Time franchise. He was first introduced in the American animated television series Adventure Time. The character was the main antagonist of the show's early seasons and develops into a main character in later seasons. He is also a main character in the adult animated spin-off series Adventure Time: Fionna and Cake.

Originally introduced as an evil but incompetent wizard obsessed with kidnapping princesses, he was depicted in later seasons of Adventure Time as a lonely man driven insane by a magical crown which grants him ice powers. The show's third season reveals that he was once an ordinary human named Simon Petrikov before falling under the influence of the crown. Simon regains his sanity and memories after being stripped of his powers by the being Golb in the series finale "Come Along with Me." Adventure Time: Fionna and Cake depicts Simon's difficulty adjusting to life after these events.

Although the character initially garnered a lukewarm reception from critics, his later backstory and character development into a tragic figure were widely acclaimed. The crown's influence over Ice King came to be seen as a complex depiction of social isolation and mental illness, notably Alzheimer's and bipolar disorder. The episodes "I Remember You" and "Simon & Marcy", focusing on the Ice King's paternal relationship with Marceline the Vampire Queen, are often considered two of the show's best.

The character was first voiced by the American actor John Kassir in the short film "Adventure Time", which introduced the character. In the short, the protagonists Finn the Human (Jeremy Shada) and Jake the Dog (John DiMaggio) fight Ice King to rescue Princess Bubblegum (Paige Moss), whom he has kidnapped. He is voiced by the American actor Tom Kenny in the television series of the same name. Kenny said that he approached the character as "a very real psychopath" who did not fully understand why his actions were wrong.

Pendleton Ward, the creator of Adventure Time, considered Ice King to be a "pathetic" character. Commenting on the character's sympathetic backstory, he said that he "enjoy[s] a villain that you fall in love with."

The journalist Neil Strauss of Rolling Stone noted that the character bore some similarities to Ward, including his "Trotsky glasses", his large beard and his strong desire for social interaction. Strauss said that "If the Ice King is Ward's dark side, then Finn, the show's 16-year-old protagonist, is his light side."

Ice King, a wizard capable of creating and manipulating snow and ice, was introduced as an antagonist of the series' main characters Finn (Jeremy Shada) and Jake (DiMaggio). A recurring plot point throughout the series is his attempts to kidnap princesses and force them to marry him, which are repeatedly foiled by Finn and Jake. Ice King rules over the Ice Kingdom, which is located in the land of Ooo where the series takes place and inhabited by penguins. About a thousand years before the start of the series, the Earth was ravaged by the Mushroom War, a nuclear conflict that mutated life and created the magical setting of Ooo.

The Ice King's heart escapes his body in "Ricardio the Heart Guy", the seventh episode of the first season, and takes on anthropomorphic features. The heart, named Ricardio (George Takei), attempts to seduce Princess Bubblegum (Hynden Walch). A weakened Ice King warns Finn and Jake of Ricardio's origins and evil nature. After they defeat him, Ice King puts Ricardio back in his body and is restored to health. Ricardio escapes from Ice King's body again in "Lady & Peebles", the 19th episode of the fourth season. Ricardio fashions a body out of Ice King's flesh, believing that it will make him more attractive to Princess Bubblegum who rejects and defeats him in single combat.