The FBI also seized the Silk Road website, replacing its homepage with a banner noting as much.
Since its 2011 inception, Silk Road has been the go-to black market for all sorts of illegal products and services. Its draw? The online marketplace offered an easy way to find goods and services -- and transact the money in secret. The site had 957,079 registered users, according to the FBI.
The site was operated on an anonymous network known as Tor, making activity on Silk Road virtually untraceable. The only money accepted on Silk Road was the digital currency bitcoin, adding an additional layer of anonymity to buyers and sellers.
Over the past two and a half years, the FBI said the site generated revenue worth more than 9.5 million bitcoins -- valued at $1.3 billion.
The FBI said Ulbricht's net worth was essentially his value in Silk Road's commissions, which totaled more than 600,000 bitcoins ($85 million).
Silk Road wasn't restricted to illegal drugs. The FBI says it was also used to trade firearms, hire assassins and employ hackers.