Who became the ruler of Marwar on 5th June, 1531, after the death of Rao Ganga?

Rao Ganga, the ruler of Marwar, died on 5 June 1531. After his death, his son Rao Maldeo Rathore succeeded him and became the ruler of Marwar.

Rao Maldeo (r. 1531–1562) is regarded as one of the most powerful rulers of Marwar. During his reign, Marwar expanded significantly and emerged as a major Rajput power in north-western India. He is also known for his conflict with Sher Shah Suri, who famously remarked that he had nearly lost the empire for a handful of millet ("a fistful of bajra").

Therefore, the correct answer is Maldeo.