The person commonly known as the Iron Man is Sardar Vallabhbhai Patel, who is the correct answer in this case. Sardar Patel played a crucial role in the Indian freedom struggle and was one of the key leaders of the Indian National Congress. He was a close associate of Mahatma Gandhi and is remembered for his efforts in integrating the princely states into a unified India after independence. He earned the nickname "Iron Man" due to his firm leadership and determination. Bal Gangadhar Tilak, Vittal-Bhai Patel, and Bipin Chandra Pal were also prominent figures in the Indian freedom struggle, but they are not commonly referred to as the Iron Man.