Betty Grof

Betty Grof is a human woman revealed to have once been the fiancée of a man named Simon Petrikov, who would much later become Ice King. She and Petrikov had a very committed relationship until Petrikov obtained an enchanted crown, which gradually began to alter his mind and body.

As revealed in "Betty," when Petrikov was wearing the crown for the first time, he chased Betty through a town while shooting ice bolts and asking "WHERE IS MY PRINCESS?" As he had said "Betty, my princess" in "Holly Jolly Secrets Part II," this likely meant he was looking for her.

It is not clear whether or not Simon had called Betty 'princess' prior to wearing the crown, or whether or not this is a name he affixed to her (much as he began calling Marceline 'Gunther') as a result of names whispered to him by the crown.

Simon presumably never saw her again after this (although he may not remember if he encountered her again as Ice King), and he records on video his desperate wish to regain his sanity so that she might one day return to him.

In "Betty," Simon, who had been changed back to normal, was able to create a portal that linked to the past before he drove Betty away. He took this moment as an attempt to apologize to Betty, but instead she leaped through the portal to be with him, only later to find out that he was dying. The cause was the being Bella Noche, who withheld all the power from the wizards of Ooo. When Simon opened the portal, it was revealed the reason she left him was because she fled when he became crazed and was attacking her with his ice powers, and then because she went forward through the time portal, explaining why Simon never saw her again in the past. She took it upon herself to get Simon's powers back and also stated that she was going to try and find a way to keep him alive and free from the crown's curse. Arriving at the castle, Betty defeated Bella Noche and restored the powers to the wizards as well as the dying Simon.

She is later seen observing Simon, now the Ice King once again, in his castle. She exits on a flying carpet (possibly to begin her search for a way to free Simon from the crown's influence alive).

Personality
Betty doesn't make an actual appearance in the series until the episode named after her. In the episode, she is shown to be very loving and devoted to Simon. She is shown to be bold and daring, as she went to face off against the creature Bella Noche by herself in an attempt to keep Simon from dying.

Like Simon, she appears to be quite educated in magical artifacts and was confident she could return Simon to normal.

Appearance
Betty is an adult woman appearing to have pinkish skin and auburn hair. In a picture on Simon Petrikov's wall, Betty is seen wearing glasses and a green turtle neck. In another picture, Betty is wearing a lab coat. This might suggest that she was in a field of study, such as science or medicine.

Trivia

 * Simon referred to Betty as his princess while he still possessed some of his sanity.
 * Betty's last name is an homage to Stanislav Grof, a psychiatrist who's one of the founders of the field of transpersonal psychology.
 * Betty appears to be left-handed since she used her left hand to punch Bella Noche, though she could be Ambidextrous.
 * She is now the second human inhabitant of Ooo.