No, it's not the Tatas, Birlas or Ambanis, it's Osman Ali Khan, the last Nizam (or ruler) of Hyderabad.
According to a new inflation-adjusted list of the world's richest people of all time, the Nizam, who ruled Hyderabad between 1886-1967, was ranked sixth with USD 236 billion.
Osman Ali Khan died in 1967 at age of 80.
Mansa Musa I of Mali