The Prime Minister of India is the head of government of the Republic of India.
Although the President is the head of all three organs of the Indian government, the real executive authority lies with the Prime Minister and his elected Council of Ministers. This is a constitutional post.
According to Part 5, Article 74(1) of the Constitution – “There shall be a Council of Ministers to aid and advise the President, with the Prime Minister as its head, and in the exercise of his functions, the President shall act in accordance with such advice, but The President may require the Council of Ministers to reconsider such advice ordinarily or otherwise and the President shall act in accordance with the advice given after such reconsideration.”