The h/h blood group, also known as Oh or the Bombay blood group, is a rare blood type. This blood phenotype was first discovered in Bombay, now Mumbai, by Dr. Y. M. Bhende in 1952.

This very rare phenotype is generally present in about 0.0004% (about 4 per million) of the human population, though in some places such as Mumbai (formerly Bombay) locals can have occurrences in as much as 0.01% (1 in 10,000) of inhabitants.

source: https://en.wikipedia.org/wiki/Hh_blood_group