Explanation:

- 'Gulamgiri' is a significant book that addresses the issues of caste oppression.

- Option 1: Ishwar Chandra Vidyasagar was a prominent social reformer, known for his efforts in women's education and the widow remarriage movement, but not for this book.

- Option 2: Narayana Guru was a social reformer from Kerala, celebrated for his work in the temple entry and caste equality movements.

- Option 3: Jyotirao Phule wrote 'Gulamgiri'. He was a pivotal figure in the fight against caste discrimination and the upliftment of lower-caste communities.

- Option 4: Ghasidas was a reformer who founded the Satnami sect, focusing on anti-caste movements in Chhattisgarh.