His friends simply call him "H," but the name Harendra Singh has been featured in news reports and court documents since his arrest in 2015 – just who is he?

Singh is at the center of a corruption scandal that will reach new heights next week. Singh is scheduled to testify against the defendants in the federal corruption trial of former Nassau County Executive Ed Mangano, his wife Linda and former Oyster Bay Town Supervisor John Venditto.

“He’s the kickoff witness, he's the Big Kahuna, he's the one everybody's been waiting to hear from,” says Newsday columnist Joye Brown.

In January, newly unsealed court documents revealed that Singh pleaded guilty to bribing Mangano and Venditto in October 2016 and agreed to testify against the former elected officials and Linda Mangano in court. Singh admitted to providing the Manganos and Venditto with thousands of dollars in bribes and kickbacks in exchange for lucrative government contracts and a $20 million loan guarantee from the town of Oyster Bay. Mangano has denied any illegal conduct for years.

So what will Singh say on the stand about what took place in his former restaurant, and in his other business dealings with the former county executive and Oyster Bay town supervisor? Joye Brown says Singh’s admission of guilt essentially guarantees the contents of his upcoming testimony.

“On one hand, you're going to have the star witness, Harendra Singh, on the stand, talking about the bribes he paid that went through,” says Brown. “And on the other side, presumably, you're going to have the defense of the three defendants going at his credibility, going at everything.”

Jury selection for the federal corruption trial of Mangano and Venditto is set to begin Monday. Singh is scheduled to take the stand Wednesday. Federal prosecutors say they expect their direct examination of Singh to last two days.