The first bitcoin billionaire is Chris Larsen according to business insider and forbes list of billionaire in cryptocurrency
http://www.businessinsider.com/bitcoin-billionaires-forbes-richest-people-in-cryptocrrency-2018-2#2-joseph-lubin-the-53-year-old-cofounder-of-ethereum-who-was-formerly-an-executive-at-goldman-sachs-has-between-1-billion-and-5-billion-in-crypto-12