Exclusive: Doppel raises $70 million Series C at more than $600 million valuation to fight AI-powered social engineering attacks

I tried to fool my brother, sort of. 

Next to him and his Pekingese on the couch, without context or introduction, I played an audio clip of me—deepfake audio of my voice that I’d asked cybersecurity startup Doppel to make. Fake Me’s voice sounded distressed, stilted, and just persuasive enough that he narrowed his eyes, scrunched his nose, and asked: “That’s AI, right?” My extremely online brother was far from fooled, but he was unsettled.

I’d asked Doppel to show me (as viscerally as possible) what deepfake audio sounded like at a moment where, as a society, we’ve perhaps never been more aware of them. The rise of generative AI-powered deepfakes has taken a technology that’s long been alarming and made it increasingly ubiquitous.

In recent months, deepfakes have been rapidly improving, said Kevin Tian, Doppel CEO and cofounder. Doppel Simulations demonstrates the state of social engineering attacks to companies, is used for training, and to test vulnerabilities.

“Our simulation capabilities are very much like vibe coding,” he told Fortune. “You give it a prompt, and that AI agent can then construct a phishing social engineering campaign that hits you specifically on your phone, maybe shoots off an SMS right after that phone call to confirm some things. Of course, you can still do the traditional phishing email…But over the past few months, what’s gotten significantly better is the ability to do real-time, synchronous deepfake conversations in an intelligent manner. I can chat with my own deepfake in real-time. It’s not scripted, it’s dynamic.”

In 2016, Tian and Rahul Madduluri met at Uber. Both eventually left and in 2022, the pair cofounded Doppel, which they started originally to help crypto companies with impersonations. But quickly, they realized the problem was a lot bigger, that “the most dangerous thing about AI is how easy it is to impersonate anyone,” said Tian. The company started to build a platform that solved that existential problem for enterprises and was listed in this year’s Fortune Cyber 60 list. 

Now, about six months after its Series B, Doppel has attracted more capital: The startup has raised its $70 million Series C at a more than $600 million valuation, Fortune has exclusively learned. Bessemer Venture Partners led the round, with participation from new investors like CrowdStrike CEO George Kurtz and NTT Docomo Ventures along with existing investors like Andreessen Horowitz, 9Yards Capital, Script Capital, South Park Commons, Sozo Ventures, and Strategic Cyber Ventures. (This Series C marks a 3x jump in valuation, the company says.)

There are some sports-associated investors also in the mix, including Aurum Partners (linked with San Francisco 49ers ownership and other LPs) and an investor group led by the WNBA’s Nneka Ogwumike, Breanna Stewart, and Kelsey Plum (via the a16z Cultural Leadership Fund). The company said it has seen 400% growth in its enterprise customer base since 2024 and that it serves “dozens” of Fortune 500 customers. Rahul Madduluri, Doppel cofounder and CTO, said via email that the round is “fuel for engineering, speed, and expansion.” But there’s a nuance—the precise goal isn’t to stop deepfakes entirely. 

“The thought process is that a deepfake is one signal. And there are actually benevolent deepfakes now, with the way enterprises are deploying deepfake technology,” said Tian. “You’ve got people using digital avatars. Like, if I were on a flight right now, I could actually use a deepfake to talk to you and share the Doppel story. So, that’s why our mission is not to stop deepfakes. It’s to stop social engineering attacks, and the malicious use of deepfakes, traditional impersonations, copycatting, fraud, phishing—you name it.”

Doppel—named for the word doppelgänger—has no shortage of competitors, including Bolster, ZeroFox, KnowBe4, and Netcraft. 

“There are a lot of legacy players who serve the space today with whom Doppel competes,” said Elliott Robinson, Bessemer growth equity partner, via email. “The overwhelming majority of these players focus on digital risk protection and security awareness training who protect against email and domain-based attacks. But they are not positioned to address today’s social engineering attack landscape.”

As Tian has worked with customers, he’s learned that there’s an area of enterprises that’s especially at-risk: Customer service. 

“It’s a vulnerable population,” said Tian. They don’t have the luxury of hanging up on a call just because it sounds suspicious. “And it’s not fair, because these people are trained to be helpful. They’re trained to take phone calls, they’re trained to respond to messages, to comply with requests, to be patient. It’s a tough job.”

Tian gets at something essential: That some of the biggest cybersecurity risks remain human, and require human training and intuition. (Perhaps something like my brother furrowing his eyebrows and deciding that audio wasn’t me at all.) 

“You can’t hard-code every role out there in the world,” he said. “You can’t get training data on every edge case in the world. So, you have to teach humans and models to reason through what’s going to be bad for your organization, and what’s safe.”

See you tomorrow,

Allie Garfinkle
X: @agarfinks
Email: alexandra.garfinkle@fortune.com
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This story was originally featured on Fortune.com