Who is Will Freeman from About a Boy and what is their importance?

Will Freeman is a rich bachelor who has never held a job. Will lives off of the royalty checks he gets for a song that his father wrote in the thirties. Will also falls in love with Rachel, a beautiful single mother who not only means romance for Will, but who also opens Will to the all the possibilities of a grownup relationship. In the end, it is Marcus who helps Will grow up even as Will guides Marcus into maturity.