Final answer:
The duty of the president is to head the executive branch of government and perform various responsibilities within that role.
Step-by-step explanation:
The duty of the president is to head the executive branch of government. The president has the power to appoint members of his/her executive cabinet to oversee major bureaucratic departments within the government. Additionally, the president serves as the civilian head of the armed forces and is responsible for setting foreign policy and influencing domestic policy and legislation.