Michael Goguen liked his privacy.

In the world of startups, full of bombast and self-promotion, the soft-spoken venture partner at Sequoia Capital specialized in quieter, more technical areas: He vetted networking, infrastructure, and security technologies for the firm before he departed abruptly last week. He spent millions of dollars to build a secluded, 32,000-square-foot getaway in Whitefish, Mont., complete with a racquetball court, underground shooting range, karate room, and 12-sided swimming pool. He kept a low social media profile, too: a bare bones LinkedIn profile, no blog, no Twitter account, and no Snapchat profile.

He also had a secret. But it turns out privacy had a price, and Goguen was not willing to pay the full amount. On March 8, Amber Laurel Baptiste sued Goguen for breach of contract, saying he owes her $30 million in addition to the $10 million he gave her in 2014. She also alleges that over the past 13 years, he sexually abused her and made her his sex slave after promising to rescue her from the human traffickers that brought her to the U.S.

Goguen, 52, says the relationship was consensual. In a graphic countersuit filed March 14, he provides what he says is e-mail and text message evidence showing she was a willing participant who became increasingly vengeful when he wouldn't make a greater commitment to her. The $40 million contract, both agree, was to stop Baptiste, 36, from going forward with a personal injury lawsuit that would have alleged he caused her bodily harm during sex. Goguen calls it extortion.

Sequoia Capital, where he had been a partner for 20 years, quickly severed all ties with Goguen and scrubbed him from their firm's site. (Goguen's lawyer, Diane Doolittle, says that it was a mutual decision to part ways.) It's now seeking replacements for him on the boards of 11 companies. In a statement, the firm said, "We didn't learn about these claims until March 10th, after they were filed in court. We understand that these allegations of serious improprieties are unproven and unrelated to Sequoia. Nevertheless, we decided that Mike's departure was the appropriate course of action."

Goguen did not respond to a request to comment for this article, but in a post on LinkedIn on Saturday, he wrote: "My departure allows me to focus with full force on clearing my name and vigorously pursuing justice."

Growing up in Bedford, Mass., Goguen loved going on hunting trips with his dad in the mountains of Maine despite temperatures that sometimes dropped to minus 10 degrees, according to an interview he gave to the Whitefish Pilot in 2012. The lanky teenager with a winning smile was attracted to highly technical engineering challenges and opted to pursue a degree in electrical engineering from Cornell University in 1986 before going on to earn his master's in the same field from Stanford University. He didn't go to business school or specialize in the high-octane networking that many other venture capitalist have perfected to build careers.

After Stanford, Goguen worked for a string of companies, including minicomputer maker Digital Equipment Corporation, which was acquired by Compaq and later merged with Hewlett-Packard. He also held positions at networking equipment company SynOptics Networking and Bay Networks—both also now defunct.

In 1996, when Goguen was 32, he joined Sequoia. One of the most respected venture firms in the world, Sequoia made a name for itself by backing Cisco, Apple, Google, and PayPal. The firm, which employs no female investing partners in the U.S., faced outrage on Twitter when, in December, Chairman Mike Moritz told Bloomberg TV that the firm wouldn't lower its standards to hire a woman partner (he later amended his statement).

The partners are tight. They meet every Monday for sometimes as long as 12 hours, and they decide all matters as a group, unlike many firms where more senior partners have the final say. Although each partner has a focus, they are slow to take credit for delivering the outsize returns that make venture capital famous.