Really the first Bitcoin billionaire will let you know him,
If it is only Bitcoin, then the first Bitcoin billionaire should be Satoshi Nakamoto.
Don't forget that he proposed bitcoin and he is also involved in the development.
So we know Winklevoss twins have over 110,000 Bitcoin. How many Bitcoins are owned by Satoshi Nakamoto whoever (he/she/they/it) is? And before you start posting numbers provide some evidence of his Satoshi's holdings too.