The book, Satyarth Prakash was written by:

The correct answer is Dayanand Saraswati. 

Key Points

• Dayanand Saraswati was born as Mool Shankar Tiwari in 1824 at Morvi (Gujarat).
• He left home at the age of 21 and lived an ascetic life for 25 years.
• He gave the slogan, ‘Go back to the Vedas’ and ‘the Vedas are the source of all knowledge'.
• He was the founder of Arya Samaj.
• He translated the Vedas and wrote three books:
  • Satyartha Prakash in Hindi
  • Veda Bhasya Bhumika, an introduction to his Vedic commentary, and
  • Veda Bhasya, a Vedic commentary in Sanskrit on the Yajurveda and Rig-Veda.