The first citizen of a country is generally considered to be the President or the Head of State. This is because the President holds the highest position in the government and represents the country both domestically and internationally. Let us analyze each option to understand why the correct answer is option 'D' - The President himself/herself.

a) The Prime Minister:
- The Prime Minister is the head of the government, not the head of state.
- The Prime Minister is responsible for running the day-to-day affairs of the country.
- While the Prime Minister is an important figure, they do not hold the highest position in the government.

b) The wife of the President:
- The wife of the President, also known as the First Lady, may hold a ceremonial role but does not have any official powers or responsibilities.
- They are not considered the first citizen of the country.

c) The father of the President:
- The father of the President is a private individual and does not hold any official position within the government.
- They are not considered the first citizen of the country.

d) The President himself/herself:
- The President is the head of state and holds the highest position in the government.
- The President represents the country both domestically and internationally.
- They have various powers and responsibilities, including being the commander-in-chief of the armed forces, signing bills into law, and appointing government officials.
- The President is considered the first citizen as they symbolize the sovereignty and authority of the nation.

In conclusion, the correct answer is option 'D' - The President himself/herself.