The Hindu ruler who built the iconic Raghunath Temple in Jammu was:

The correct answer is: a) Gulab Singh.

Gulab Singh was the Hindu ruler of Jammu and Kashmir from 1846 to 1857. He was the founder of the Dogra dynasty, which ruled Jammu and Kashmir until 1947. Gulab Singh was a powerful and ambitious ruler who expanded his kingdom significantly during his reign. He is also known for his patronage of the arts and architecture. The Raghunath Temple is one of the most important temples in Jammu and Kashmir. It is dedicated to the Hindu god Rama. The temple was built in the 19th century by Gulab Singh. It is a beautiful example of Hindu architecture.

The other options are incorrect because:

• Ranbir Singh was the son of Gulab Singh and the ruler of Jammu and Kashmir from 1857 to 1885.
• Pratap Singh was the son of Ranbir Singh and the ruler of Jammu and Kashmir from 1885 to 1925.
• Hari Singh was the son of Pratap Singh and the last ruler of Jammu and Kashmir. He ruled from 1925 to 1947.