It has cost the world’s biggest banks $9 billion to settle allegations over the rigging of Libor, a globally important interest rate benchmark. Now, an individual is finally facing trial over the affair.

On Tuesday, a British court began hearing evidence in the trial of Tom Hayes, a former trader at UBS and Citigroup’s Tokyo branch who prosecutors say served as the “ringmaster at the very center” of the Libor manipulation scheme.

Prosecutors told the court that Hayes “behaved in a thoroughly dishonest and manipulative manner by repeatedly cheating those with whom he had extended into huge commercial transactions,” the Wall Street Journal reports. Hayes has pleaded not guilty, and his defense has not had the chance to respond to allegations.

Libor, an acronym for the London Interbank Offered Rate, serves as a baseline interest rate for more than $300 trillion in financial products and contracts, including student loans, mortgages and credit cards, as well as more bespoke instruments like interest rate swaps.

Between 2003 and 2012, traders at more than a dozen of the world’s largest banks colluded in chat rooms to manipulate the Libor rate, which was then set daily by committee, for their own profit -- and to the detriment of their clients.

More than 100 bank employees have lost their jobs since the scandal reared its head in 2012, but Hayes is the first individual to face trial. In a 2013 text message to the WSJ, Hayes wrote, “This goes much higher than me.”

Prosecutors have cast Hayes as a central figure in the Libor scheme, motivated by greed and dishonesty. In 82 hours of taped interviews with the U.K. Serious Fraud Office, prosecutors say Hayes admitted to his role in the conspiracy and turned over the names of other traders, including his half-brother, a banker at HSBC.

In his role in the Libor affair, Hayes allegedly cajoled fellow traders and other middlemen into using his fudged numbers. The head prosecutor, Mukul Chawla, said Hayes’ actions “struck at the very integrity” of the benchmark, the Financial Times reported.

In interviews, prosecutors say Hayes was recorded explaining how his attempts to manipulate Libor stemmed from the pressures of generating profits for the bank and for himself. “I was operating within a system in which it was commonplace,” Hayes said in the recordings.

Manipulating Libor for a profit, Hayes went on, “had some impact on me as an individual, both my seniority within the bank, my standing within the bank, my potential remuneration.”

The trial, which is expected to last 10 weeks, continues Wednesday.