The correct answer is option 3, Balaji Baji Rao. He was popularly known as Nana-Saheb. Let`s understand why this is the correct answer by dissecting the other options:

Option 1, Balaji Vishwanath: He was the first Peshwa of the Maratha Empire, serving from 1713 to 1720. Although he played a significant role in expanding Maratha influence and consolidating power, he is not known as Nana-Saheb.

Option 2, Baji Rao: He was the second Peshwa of the Maratha Empire, serving from 1720 to 1740. He was a renowned military leader and expanded the Maratha Empire to its peak. However, he is not known as Nana-Saheb.

Option 4, Madhav Rao I: He was the fourth Peshwa of the Maratha Empire, serving from 1761 to 1772. He is remembered for his administrative reforms and rejuvenation of the Maratha Empire, but he is not known as Nana-Saheb.

Based on the above analysis, option 3, Balaji Baji Rao, is the correct answer as he was popularly known as Nana