Rick Gates, Paul Manafort’s former right hand man, has been called to testify in the trial the former chairman of Donald Trump’s presidential campaign.

Gates pleaded guilty in February to a bank fraud conspiracy charge in exchange for testifying against his former boss.

Experts have billed Gates as the star witness in the tax evasion and bank fraud trial that Special Counsel Robert S. Mueller III is prosecuting against Manafort who is facing 18 counts of tax evasion.

The defense has accused Gates of embezzling millions of dollars from Manafort, claiming he had sweeping authority over his boss’s business and personal expenses and that he abused that authority by going behind Manafort’s back to deceive his bookkeeper and the accountants who prepared Manafort’s taxes.

On the prosecution’s projected evidence list are 23 email exchanges between just Manafort and Gates.