One of the first witnesses in the gender discrimination case brought by former partner Ellen Pao against Kleiner Perkins Caufield & Byers will be Trae Vassallo.

She’ll be called to support Pao’s side of the story in a closely watched gender discrimination and retaliation suit that kicked off today in San Francisco.

Vassallo is the well-respected former Kleiner Perkins partner who helped lead investments in Nest, Dropcam and Opower (the former two were bought by Google for $3.2 billion and $555 million, respectively, and the latter went public last year). She stepped back from the firm after a reorganization last year left her out of the committee responsible for investments.

In Pao’s original complaint, Vassallo had been cited as an unnamed fellow female junior partner who was also inappropriately approached by Ajit Nazre, the former partner with whom Pao had a sexual relationship, after which she alleges he repeatedly retaliated against her.

Kleiner Perkins has rejected Pao’s claims of gender discrimination and retaliation by alleging that she was an underperforming employee, and that her treatment did not stem from her gender.

Vassallo’s presence will therefore be important as someone who was reportedly viewed as a “cooperative team player” within Kleiner Perkins, but who was also upset about how the firm handled her reports about Nazre’s overtures to have a romantic relationship with her.

According to Pao’s attorney Alan Exelrod, who delivered an opening statement today, Nazre had approached Vassallo in 2009, allegedly putting his leg on her at a work event. She rejected him, though did not report it to the firm until 2011. The firm did not honor Vassallo’s request to remove Nazre from his assignment as her primary performance reviewer. Then Nazre allegedly invited Vassallo to a business dinner in New York with former DoubleClick CEO David Rosenblatt, which was a “lie,” according to Exelrod, and instead was an excuse for him to proposition her. According to Exelrod, Kleiner Perkins partner Ray Lane’s response to Vassallo complaining about that encounter was “You should be flattered.” The firm launched an internal investigation that found Vassallo’s story was credible.

The Kleiner Perkins defense team has said it will present evidence that Pao and Nazre’s relationship was consensual, which would make it significantly different from what happened between Vassallo and Nazre.

In 2011, Vassallo and Pao were not promoted from junior partner to senior partner, while three of their fellow junior partners — all male — were.

Pao’s legal team has not publicly released a list of witnesses. Jury selection in the trial was completed Monday and opening statements were offered Tuesday. The trial is expected to last about a month.