The person who is popularly known as Deshbandhu is Chittaranjan Das. Deshbandhu, which means "Friend of the Nation" in Hindi, was a title given to Chittaranjan Das due to his immense popularity and significant contributions to the freedom movement in India.

Option 1, Aurobindo Ghose, was an Indian philosopher, poet, and nationalist who played a key role in the Indian independence movement. However, he is not commonly referred to as Deshbandhu.

Option 3, G.B. Pant, was an Indian politician and statesman who served as the Chief Minister of Uttar Pradesh and later as the Home Minister of India. He is not known as Deshbandhu.

Option 4, R.M. Lohia, was an Indian socialist political leader who advocated for social equality and played a significant role in the Indian independence movement. However, he is not commonly referred to as Deshbandhu.

Overall, the correct answer is option 2, Chittaranjan Das, who is popularly known as Deshbandhu for his important role in the freedom movement in India.