There are two birthdays to recognize today.
First, we extend birthday wishes to Jagdish Bhagwati. Professor Bhagwati is at Columbia University and is one of the leading international economists today. His work is very accessible, one of my favorites being In Defense of Globalization. For a sample of his work, look here.
The second birthday we recognize is that of Alfred Marshall. If you aren't sure why we should recognize Marshall, look at the supply and demand graph you most recently drew. It was Marshall who emphasized that price was the result of BOTH. He was also the thinker behind price elasticity and consumer surplus. For a more complete bio, check here.