The character Jamie Sullivan was based upon Nicholas Spark's late sister Daniel Sparks Lewis. Danielle died a few years ago (April, 2000) of a brain tumor which was in-operable. The Jamie in the book was a lot like her. All she had ever wanted out of life was to get married, and even though she was going to die, her boyfriend asked her to marry him anyway. [Daniel was about 15 years older than Jamie, however.]
Jamie is named for his editor at Warner Books, Jamie Raab.
On his website, Nicholas Sparks explains his inspiration for Jamie (from a speech given in Berlin, Germany for Heyne Verlag, 2000):
A Walk to Remember was inspired by my sister.
In many ways, Jamie Sullivan was my younger sister. Like Jamie, my sister was sweet. Like Jamie, my sister had tremendously strong faith. Like Jamie, my sister loved church. Like Jamie, my sister wasn't popular at school. Like Jamie, my sister was always cheerful. Like Jamie, all my sister wanted in life was to get married.
And like Jamie, my sister got cancer.
Like Jamie, my sister met someone. And like Landon, there was a long period of time when this fellow couldn't imagine himself marrying a girl like her. And yet, in the end, he couldn't help himself. Even when he knew she was sick, even when he knew that she might not make it, this man asked my sister to marry him.
It was just about the sweetest thing that's ever been done for anyone, and I suppose I wrote this novel not only so that you could get to know my sister, but so that you would know what a wonderful thing it was that her husband once did for her.
Sadly, my sister died in June (2000). She was thirty-three years old. . ."