The directors of on board of directors are essentially representatives of the shareholders of the company elected by them to manage the overall affairs of the company. Thus the primarily responsibility of directors is to safeguard and promote the interest of the shareholders in the company. Indirectly it also means ensuring that the company is meeting all its legal and moral obligation toward all other stakeholders of the company including the environment within which company operates.
If all the directors performed this role of representative of shareholders sincerely and honestly, there would be no additional requirements of corporate governance or ethical conduct. The problem of corporate governance arises because the directors may and some times do deviate from this primary duty towards the shareholders to promote their personal interests. Many times such deviation from the ideal path are clearly illegal, and therefor covered by relevant legal provisions. But there are other areas where the directors need to use their personal discretion and judgment in the interest of the company. Most of the failure of corporate governance and ethical standards take place in this area.
The basic need is for the directors to be honest and sincere towards their obligation towards the shareholders. However, many times greed has an upper hand over honesty. All that directors have to maintain high standards of corporate governance and ethics is to keep their greed in check.