Balaji Vishwanath, popularly known as Peshwa Balaji Vishwanath was the first Peshwa (or Principal Minister) from the Brahmin family of the Maratha Empire during the 18th century. Hence he was called the founder of the Peshwas.
Baji Rao was the son of Balaji Vishwanath became Peshwa upon the death of his father. He was known as the fighting Peshwa because:
1) He fought over 41 major battles and had never lost a battle.
2) He moved the administrative capital of the Maratha Empire from Satara to the city of Pune in 1728.
3) He fought for the protection of Hindu Dharma and frees Central and Western India from Mughals.
4) During his tenure, the Marathas defeated the Siddis (Moghul Admirals), Portuguese, Nizam and other generals.