Answer:
At the Madras Session of the Indian National Congress in 1927, when the Congress boycotted the Simon Commission, the Congress President was MA Ansari.

Background:
The Simon Commission, officially known as the Indian Statutory Commission, was appointed by the British government in 1927 to discuss constitutional reforms in India. However, the Commission did not include any Indian members, which led to widespread protests and boycotts by the Indian National Congress and other nationalist organizations.

Role of MA Ansari:
MA Ansari, also known as Maulana Mohammad Ali Ansari, was an Indian nationalist leader and politician. He was the President of the Indian National Congress during the Madras Session in 1927. As the Congress President, Ansari played a crucial role in leading the party's decision to boycott the Simon Commission.

Reasons for the Boycott:
The Indian National Congress decided to boycott the Simon Commission for several reasons:

1. No Indian representation: The Commission consisted entirely of British members, which was seen as an affront to Indian aspirations for self-governance.

2. Lack of consultation: The British government did not consult Indian leaders before forming the Commission, undermining the democratic principles of representation and participation.

3. Protest against colonial rule: The boycott of the Simon Commission was also a broader protest against British colonial rule in India and a demand for greater autonomy and independence.

Impact of the Boycott:
The boycott of the Simon Commission was a significant event in India's struggle for independence. It highlighted the growing discontent and demand for self-rule among Indians. The boycott also led to increased unity and mobilization within the Indian National Congress and other nationalist organizations.

Conclusion:
MA Ansari, as the President of the Indian National Congress, played a crucial role in leading the party's decision to boycott the Simon Commission. The boycott was a powerful statement against British colonial rule and a significant step in India's journey towards independence.