A year ago Bitcoin price reached $20.000. A lot of people tried to explain why this happened but nobody is 100% sure. A user called Bitfinexed started to write about the connection between Tether and Bitfinex, they are actually the same company, and discovered some disturbing facts. Tether is a stablecoin and supposedly for every Tether coin out there there is a dollar at Tether's bank account. They claimed many times that they were audited by different companies but it was a lie. Finally when they decided to accept a control, they fired the guy because it was taking a lot of days to complete the control! In a few words, what they did is create millions of coins and use it to buy Bitcoin. Then they sold it making hundreds of millions in profit. And all this was done on Bitfinex. It is a very interesting story and I suggest you read the blog at:
https://medium.com/@bitfinexed
and follow him on Twitter
https://twitter.com/bitfinexed