The trial of Sam Bankman-Fried, former CEO of one of cryptocurrency's biggest exchanges, began Tuesday with a jury set to determine if he committed massive fraud by stealing billions of dollars from clients.

The 31-year-old — once one of the most respected figures in crypto — now faces decades in prison and could see his name stand alongside Bernie Madoff and Elizabeth Holmes as the era's most prominent fraudsters.

The first day of the trial was devoted to jury selection for a case that is set to last about six weeks. Bankman-Fried faces seven counts including wire fraud, securities and commodities fraud, and money laundering.

He risks more than 100 years behind bars if he is found guilty on all charges.

Bankman-Fried entered the courtroom alone — without being escorted by security guards — uncuffed, and took his place alongside his lawyers, an AFP journalist observed.

Dressed in a dark suit and striped tie, his usually long curly hair was cut short, reportedly by a fellow inmate at the Brooklyn jail where he is being detained.

"You have the right to testify in your defense in this case. The decision is up to you," US District Judge Lewis Kaplan told Bankman Fried.

In just a few years, the Massachusetts Institute of Technology graduate turned his FTX platform into the world's second-biggest crypto exchange, making him a tech world billionaire wunderkind.

FTX became a global name through a marketing campaign that included celebrity partnerships with stars such as supermodel Gisele Bundchen and basketball legend Stephen Curry, and buying the naming rights for the home arena of the Miami Heat basketball club.

Bankman-Fried also stepped in as a kind of savior of the industry when other crypto companies faced difficulties, with FTX swooping in to offer a financial lifeline.

At the height of his career, Bankman-Fried was thought to be worth $26 billion as he attracted droves of small investors to invest in cryptocurrencies such as Bitcoin or Ethereum.