He is best known for his dubious role in the Vietnam War and also, now, through the movie The Fog of War. But McNamara also had a huge influence on the economics profession, most of all through his 13-year presidency at the World Bank. He focused the Bank on poverty reduction, he brought Communist China into the Bank, he introduced the practice of five-year lending plans, he significantly increased the Bank's budget, he grew staff from 1600 to 5700, he favored sector-specific research, he raised money from OPEC, he strongly encouraged "scientific project evaluation," and he started a largely successful program to combat "river blindness"; the latter may have been his life's achievement. The Bank as a large, modern technocracy — for better or worse — dates largely from his tenure.
He probably shaped the Bank more than did any other single person. Here is one overview. The Bank, of course, continues to be a major employer of economists and a major influence on the theory and practice of development economics.
Addendum: Kevin Drum offers some interesting thoughts.