To some degree, it is unfortunate that those who run projects are referred to as managers because there is so much involved in being a truly excellent project manager.
Almost all project literature will list the following as, at least, the core and most important characteristics of a project manager:
Ability to influence the organization
The traditional view of management and leadership is that management is concerned with efficiently and effectively using a company’s resources to accomplish the company’s business, while leadership is more concerned with innovation, challenging the status quo, and broadening the company’s outlook and capabilities. Managers try to get people to agree about the things that need to be done. As Warren Bennis and Burt Nannus (professors at the University of Southern California) so succinctly describe the difference between managers and leaders; “Managers are people who do things right and leaders are people who do the right thing.” 
Project managers have three basic responsibilities in managing a project: to be on or under budget, to be on or ahead of schedule, and to meet the customer’s performance criteria. So it makes sense that project managers must have management skills to accomplish the project’s goals successfully. But management skills without leadership skills are very likely to lead to poor results or even failure.
An in-depth study identified a number of characteristics important in a leader.  The top four characteristics were: honesty, competence, the ability to look forward, and inspiration.
Communication skills are important for any manager. For the project manager, they are absolutely critical. When one considers the amount of time a project manager spends communicating with his team, the project sponsor, stakeholders, and senior managers throughout the organization, it becomes readily apparent that a poor communicator has almost no chance of completing the project as planned. The project manager requires not only excellent speaking skills, but writing skills as well. This is because a large percentage of communication is in the form of reports. When I think of how important communication skills are in project management, I am often reminded of a classmate who, when he discovered that he was required to take a speech class, exclaimed that he was studying to be an engineer, not a speaker. In today’s business world, there are very few professions in which success does not depend on how well the practitioner communicates.
Negotiating skills rank closely with communications skills in importance, and indeed one cannot be a successful negotiator without possessing excellent communication skills.
Project managers are constantly faced with issues relating to scope, cost, and schedule objectives, organizational objectives relative to the project goals, changes to the scope, resource assignment and allocation, and team conflicts.
Many project managers also are involved in contract negotiations. If a project is the result of an external contract, it is not unusual for the project manager to have been a part of the negotiation team. Likewise, the project manager usually is a part of the negotiation team when hiring vendors, or when teaming with other companies to pursue a project.
Problem solving is more than evaluating a problem and determining a solution; it also involves making a decision.
Project problems can be the result of technical incompatibilities or even the lack of a technical capability. They can be interpersonal in nature or they could result from functional managers reassigning one or more of the resources. They also can take the form of external difficulties with environmental or other regulating agencies. Whatever the source, it is the project manager’s responsibility to assess the problem and determine the best course of action to resolve it. Finding a solution to a problem, though, is only half the job. A decision about how or even whether to implement the solution must be made.
Decision making usually involves investigating several options and choosing the best solution for the problem and the good of the project.
Ability to Influence the Organization
Most people avoid using the word politics when speaking of their job. The fact is, though, that polishing and exercising one’s political skill is crucial to success, especially in dealing with stakeholders. The project manager’s influence in an organization can be fragile at best, but exercising his political skill is one way to build influence.
Assess the environment. The environment of the organization is determined by the corporate culture, so the project manager must be sensitive to the corporate goals and strategies and who the relevant stakeholders are.
Identify the goals of the principal actors. Making sure the project goals are consistent with those of the stakeholders is the surest way a project manager can obtain and keep them as allies. To understand a stakeholder’s goals means asking: “What drives this person? Does she have a hidden agenda? If so, how can I deal with this hidden agenda?”
Assess your own capabilities. Successful project managers know their own strengths and weaknesses and how best to capitalize on their strengths. Once the project manager identifies the stakeholders and their goals, he has to act to mitigate any negative feelings or reservations about supporting the project.
These three steps—assessing the environment, identifying the goals, and assessing your own capabilities—are the basis of increasing political awareness about the culture in the organization, and is one way to increase your influence in the company.
Credibility means that the project manager is known to be a person of integrity, knowledgeable, capable, and dependable. A reputation for credibility is earned; it cannot be established overnight, and it will not be believed until it is demonstrated. This quality is something that the project manager must work at with patience and persistence. The only way to be credible is to deliver as promised, be honest in all dealings, and be consistent in behavior.
Almost every other mistake a person makes can be overcome and forgiven—but not dishonesty. Once a person lies, no one fully trusts her again, and her credibility disappears.
Ethical behavior has become so important in project management that the Project Management Institute (PMI) requires every PMI member to sign a Project Management Code of Ethics. In fact, one of the surest and fastest ways for a Project Management Professional (PMP) to lose her certification is to exhibit unethical behavior.
Ethical behavior simply defined means to do what’s right. Yet, many professional project managers will risk damaging their credibility and violate their ethics rather than admit that they are having a problem with a project. This is a serious failing.
A major problem, though, is that the project manager is sometimes caught in the difficult situation of being directed by a senior manager not to reveal a problem to a customer. The rationale is that the problem will be corrected without the customer’s ever being the wiser. In this situation, you have to evaluate your ethical code and decide whether your conscience will allow the lie, and if you are willing to risk your professional reputation.
Certainly some judgment is required about the seriousness of a problem and whether it is a breach of ethics not to inform the customer. Every project suffers daily snags, irritations, and false starts. The customer will not be interested in these problems—they are the normal difficulties encountered in running a project. However, if the problem is severe enough to cause a delay or requires a short-term infusion of additional resources, the customer needs to know about it. The customer will not be upset that the project encounters a problem, but she will be very upset to learn of the problem after it is so big that there is a significant impact on the project. Customers typically accept problems as long as they can be a part of the solution.
W.G. Bennis and B. Nannus, Leaders: The Strategies for Taking Charge (New York: Harper & Row, 1985).
James M. Kouzes and Barry Z. Posner, The Leadership Challenge (San Francisco: Jossey-Bass, 1989).