The backstory of Adventure Time's Ice King makes him one of the most tragic characters on the show. Adventure Time debuted back in 2010 and is animated show following the adventures of human Finn and his shape-shifting dog Jake. The series takes place in the Land of Ooo, which is home to any number of magical creatures, including vampires, sorcerers, and demons. The Ice King - not to be confused with Game Of Thrones' Night King - is one of the main antagonists.
Adventure Time ran for ten seasons, coming to an end in 2018. The series finale "Come Along With Me" proved to be an emotional ending to the show but while the Adventure Time season 11 comic that followed continued the story of Finn and Jake, the creators of the show consider it non-canon. There was also talk of a potential movie version, though there has been little sign of movement on the project since the show ended.
Adventure Time is positively packed with lore and backstory, and the show has tackled some mature themes too. This can be seen with the Ice King, who was first presented as a cartoony villain obsessed with kidnapping Princess Bubblegum, but later seasons would greatly flesh him out. Before the outbreak of the apocalyptic Mushroom War, the Ice King was an antiquarian named Simon Petrikov. Simon was engaged to a woman called Betty Grof but following his discovery of a mysterious crown in Scandinavia, his destiny was changed forever.
Wearing the crown caused visions and blackouts, which led Betty leaving Simon. Over time, the crown altered his body and mind, causing him to gradually forget his old life. He also met young vampire Marceline following the outbreak of the Mushroom War. He became her protector for a time, risking his life to keep her safe, which sometimes involved using the power of the crown and eroding his sanity further. He also gave her a doll named Hambo to comfort her, which became her favorite possession. Simon decided to leave Marceline when he became afraid of what the crown was turning him into and that he could hurt her without being aware of what he was doing.
Following this, Simon essentially disappeared and transformed into the Ice King. While the character might be cartoonish on Adventure Time, he's also shown to be riddled with loneliness and desperate to be loved. Most of his evil deeds throughout the series are driven by this and the Ice King appears to have little to no memory of his previous life. It's revealed later in the series that Betty dedicated herself to freeing Simon of the crown's influence and became a wizard. In the Adventure Time finale, she helps summon an evil deity known as GOLB to the Land of Ooo.
The Ice King tries to talk her out of her plan, which leads to him, Betty, and Finn all being swallowed by GOLB. Once inside, their powers are absorbed by the deity, causing the Ice King to become Simon again. Sadly, his reunion with Betty is shortlived, as she kicks him and Finn out of the creature and makes a wish that saves the world. This also causes her to fuse with GOLB, who soon exits Ooo. While this is a bittersweet ending to the character's journey on Adventure Time, at least he's free of the crown and free to lead a normal-ish life.