In Sean ‘Diddy’ Combs’s Trial, Cassie Is the Star Witness

The identity of the individual referred to in waves of dramatic legal filings as Victim-1 — the woman at the very center of the racketeering conspiracy and sex-trafficking case against the music mogul Sean Combs — was never much in question.

But when she takes the witness stand at a Manhattan courthouse under her own name this week, there will be little doubt that there would not have been a criminal indictment against Mr. Combs without the testimony of Casandra Ventura.

A singer and model known mononymously as Cassie, she was Mr. Combs’s on-and-off girlfriend — and employee — almost from the time they met in 2005, when she was 19, until she finally severed ties from his storied record label, Bad Boy, in 2019.

After months of preparation and anticipation, Ms. Ventura, now 38, is expected to recount for the jury how Mr. Combs instituted a system of abuse and control over her life and career for more than a decade. Prosecutors say the executive dangled ever-disappearing music opportunities; beat her when she stepped out of line; and plied her with drugs, forcing Ms. Ventura to have marathon sex sessions with male prostitutes while he taped the encounters.

Lawyers for Mr. Combs have portrayed the relationship as loving but deeply toxic and complex, prone to infidelity and mutual abuse, while maintaining that any sexual arrangements were completely consensual. They depict Ms. Ventura as a bitter ex and extortionist who sought only a payday, not justice.

What both sides cannot disagree about is that it was Ms. Ventura’s decision in late 2023, following extensive therapy, to pour her allegations into a federal lawsuit — and Mr. Combs’s choice not to settle the dispute before it became public — that led to this moment, in which Mr. Combs, 55, has fallen from a beloved billionaire celebrity to an inmate facing a potential life sentence.