He was the father of John Stuart Mill, but he was an economist in his own right, and a friend of Jeremy Bentham and David Ricardo. While not known for many original contributions to the field, he helped to popularize many ideas such as Bentham’s utilitarianism. And today is the anniversary of his birth.
If you've read about John Stuart Mill, you are aware of the impact his father had (for good and for ill) on his life and intellectual development.
Read more about James Mill here and here.