A CEO (Chief Executive Officer) is the top-ranking individual employee within an organization. They are an employee in the sense that they work for the firm (as opposed to being elected by shareholders), but he or she is not a run-of-the-mill staff member; they have considerable responsibility and influence within the firm.
Having said that, in organizations with a healthy corporate governance function, the Chief Executive Officer is also not an all-powerful leader with unchecked power and decision-making authority. The CEO reports directly to, and is ultimately accountable to, the firm’s Board of Directors (the members of which are elected by shareholders).
Specific responsibilities of a CEO may vary slightly from one company to another, but, in general, this individual is responsible for the ultimate success or failure of the organization.