In a recent blog post the Ice King was revealed to be Simon Petrikov. I was wondering if the details of his transformation are in the cartoons, and either way what they were?
The third tape reveals that a long time ago (possibly prior to the Mushroom War), the Ice King was a human named Simon Petrikov, who had a fiancée named Betty. He was an antiquarian, and purchased a strange crown from a dock worker in Scandinavia. He took the crown home to show Betty, and when he put the crown on his head for a laugh, he started to see visions and hallucinations. He fought with them, shouted at them before realizing it was the crown sending the visions into his head. He quickly took it off after his realization, he had no recollection of his actions, but what transpired during that time eventually caused Betty to leave him (Simon noted, after taking off the crown, she was "Looking at me with such contempt.") As the video progresses, Simon begins to look more and more like the Ice King as we know him. His skin takes on a blue tint, his hair begins turning white, his nose starting to be pointy and a beard slowly appears on his face. He is increasingly distraught about the loss of Betty, his "princess", and his actions while under the influence of the crown. In the background of the video, we see an airplane flying over modern buildings, evidence of his life before the Mushroom War. Simon is aware that he is losing his mind, yet is unable to control it. In the end, he is accepting of his fate, and he begs for forgiveness for his actions to anyone who might come across his tapes.