Step 1: Understanding the Question:
The question asks for the founder of the "Arya Samaj," which was a highly influential socio-religious reform movement in modern Indian history.
Step 2: Detailed Explanation:
1. The Arya Samaj was founded on 7 April 1875 in Bombay (now Mumbai) by Swami Dayanand Saraswati.
2. Swami Dayanand Saraswati (1824–1883) was a renowned Sanskrit scholar, ascetic, and social reformer who advocated for a return to the pure Vedic tradition.
3. He rejected modern corruptions of Hinduism such as idol worship, child marriage, animal sacrifice, and the hereditary caste system, promoting monotheism and female education instead.
4. He coined the famous slogan "Go back to the Vedas" (Vedo ki aur lauto) and authored the book "Satyarth Prakash" (The Light of Truth) to spread his philosophy.
5. Looking at the other options:
Raja Ram Mohan Roy founded the Brahmo Samaj in 1828 to reform Hindu society and challenge practices like Sati.
Swami Vivekananda was a disciple of Ramakrishna Paramahansa who founded the Ramakrishna Mission in 1897 to promote humanitarian and social work.
Keshab Chandra Sen was a prominent reformer associated with the Brahmo Samaj, who later established the Brahmo Samaj of India in 1866.
6. Thus, Swami Dayanand Saraswati is the correct founder of the Arya Samaj.
Step 3: Final Answer:
Swami Dayanand Saraswati was the founder of the Arya Samaj.