Caroline Ellison is a math whiz, trader, and shadow figure behind FTX's collapse. She's testifying this week in the criminal trial of her ex-colleague and boyfriend, Sam Bankman-Fried.

Caroline Ellison was the CEO of Alameda Research, a trading firm launched by Sam Bankman-Fried. She expected to testify in SBF's trial this week.Tyler Le, Jenny Chang-Rodriguez/Insider

• Caroline Ellison was the CEO of Alameda Research, a trading firm launched by Sam Bankman-Fried.
• She oversaw bets Alameda took with customer funds. She pleaded guilty to seven criminal counts.

As Sam Bankman-Fried's crypto empire began to unravel last year, his colleague, now 28-year-old Caroline Ellison, emerged as a figure of intrigue and speculation.

In August 2022, Ellison became the head of Alameda Research, Bankman-Fried's trading firm that was closely intertwined with his crypto exchange, FTX. By November, as FTX swiftly spiraled into bankruptcy, Ellison began to draw attention for her role in overseeing the risky bets Alameda took with customers' funds. She's since pleaded guilty to seven charges and has struck a deal to cooperate with federal prosecutors.

Over the past several months, Ellison has largely retreated from the public eye, even while Bankman-Fried — whom she occasionally dated in prior years — remained active on the media circuit. Now, as the trial of Bankman-Fried enters its second week, Ellison will testify as a key witness.

Here's what we know about Caroline Ellison.