Secondly, it's shows a shifting of priorities for a Silicon Valley venture capitalist to be putting money into anything but a start up - many thought cryptocurrencies weren't really on their radar until now.
Thiel's fund has already announced hundreds of millions of dollars in profit thanks to 2017's meteoric rise in Bitcoin value, from about $1,000 per coin to almost $20,000.
During the fourth quarter of 2017, Bitcoin experienced nearly unprecedented gains in value, rising briefly to more than $19,000 before adjusting to close the year trading slightly under $14,000.
Tech Billionaire Trump Backer Peter Thiel Also A Big Investor In Bitcoin
Bitcoin on the other hand jumped about 1,400% in 2017.
Founders began buying into bitcoin before the recent volatility, and the decision was made by Thiel and Founders' other investment partners, the unnamed sources told the Journal.
The investments by Thiel's fund, which WSJ said was between 15 and 20 million dollars, would be worth hundreds of millions today, given the appreciation in the price of bitcoin.
The VC firm confirmed to Bloomberg that bitcoin infrastructure companies such as BitPay, BitGo, Polychain and MetaStable are in the firm's portfolio, but declined to comment on the firm's ownership of bitcoin.
Conversely, if the bitcoin price were to tank and never recover in the coming months, Thiel and the Founds Fund will have been burned in more ways than one.
Bitcoin's second trading session of 2018 has seen the controversial cryptocurrency rise by as much as 15%.
The price of Bitcoin has been on a roller coaster ride rising from less than a thousand dollars at the beginning of 2017 to about $20,000 at one point several weeks back.
Peter Thiel earlier this year warned that people were "Underestimating" Bitcoin.
Of cryptocurrencies at large, he said, "While I'm skeptical of a lot of them, I do think people are a little underestimating Bitcoin specifically".