There are only 43 people known to have been RHnull, but the actual number is expected to be much higher. Rhnull phenotype is a rare blood group with a frequency of approximately 1 in 6 million individuals.

Considering our current world population of 7,714,576,923 people (2019 estimate), 1 in 6 Million individuals being RHnull would come to around 1,286 people worldwide being RHnull.

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James Harrison, the best know RHnull person due to having saved millions of babies' lives.

See also:

What is Rh null?

Wikipedia