On many NFL teams, general managers are the eyes and ears of the owner, and they oversee the day-to-day operation of the team. They must be cold and calculating people because they have to make a lot of difficult personnel decisions.
They make the player trades and free agent acquisitions, decide salary levels, and ultimately determine which players to select in the NFL draft. General managers must be excellent judges of every player's ability because they're responsible for doing what's best for the organization. They must have a feel for what the team needs and be able to work in conjunction with the head coach and his needs.
The best possible scenario is to have a solid general manager and a great head coach, who can put their egos aside and work together. But this situation is very rare these days because head coaches usually want total control over personnel, like Pete Carroll has in Seattle.
General managers oversee a large front-office staff. Some teams have business, marketing, and public relations personnel. People reporting to the general manager include the following: capologists (who monitor a team's salary scale within the salary cap), business managers, contract negotiators (also known as a club vice president), human resources directors, and public relations directors.