Global risk and intelligence firm led by former U.S. Secret Service and FBI leaders becomes Mainstreet’s eighth operating company and anchors a new security and intelligence vertical

Mainstreet Holdings, the AI-native permanent capital holding company valued at more than $4 billion, today announced it has acquired Sentinel, a global risk and intelligence firm led by former senior officials from U.S. law enforcement and intelligence agencies. The deal adds a new vertical to Mainstreet’s portfolio, which has verticals in software, financial services and workforce businesses.

Charles Marino founded Sentinel in 2017. He is a former Supervisory Special Agent who served in the U.S. Secret Service under three Presidents. Sentinel advises Fortune 500 companies, professional sports organizations and high-profile executives on threats before they happen. Its services include executive due diligence, continuous threat monitoring, live event intelligence and digital protection.

“Trust is the one asset every business we own depends on, but in today’s environment, trust alone is no longer enough,” said Jesse Tinsley, Founder and CEO of Mainstreet. “The greatest risks aren’t always the ones you can see. Chuck has spent decades building the relationships, judgment and intelligence necessary to identify threats before they become crises. That kind of institutional knowledge can’t be replicated with technology or capital alone. By combining Sentinel’s world-class intelligence capabilities and trusted relationships with Mainstreet’s AI-powered operations, technology infrastructure and expansive customer network, we have an opportunity to redefine what modern security and intelligence services look like, making Sentinel even more effective, scalable and accessible to thousands of organizations that have never had access to this level of protection.”

“For nearly a decade, our team has helped leaders see risk early and act with confidence in an increasingly volatile world,” said Charles Marino, Founder and CEO of Sentinel. “Mainstreet is a permanent owner, not a financial buyer looking for an exit. That gives us the backing to scale our team, invest in technology and serve more clients without compromising the discretion they rely on.”

Sentinel will keep its brand and continue to be led by Marino and its current leadership team. The transaction closed in October 2026. Terms of the deal were not disclosed.

About Mainstreet Holdings

Mainstreet is an AI-native permanent capital holding company that acquires and operates durable software and services businesses. Its portfolio includes Recruiter.com, Employer.com, BountyJobs, Bench, MainStreet Tax Credits, Capbase and Sentinel. Mainstreet brings each company onto a shared AI-powered operating platform, holds its businesses indefinitely and reinvests their cash flow into further acquisitions. The company is backed by Greylock, Accel, SignalFire, Moxxie Ventures, and Deel, among others. Founders and advisors considering a sale can contact corpdev@mainstreet.com or visit https://mainstreet.com.

About Sentinel

Sentinel is a global risk and intelligence firm led by former leaders of the U.S. Secret Service, FBI and intelligence community. It gives corporations, institutions and high-profile individuals discreet intelligence they can act on. Learn more at http://sentinel.security.

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"Trust is the one asset every business we own depends on, but in today's environment, trust alone is no longer enough." Jesse Tinsley, Founder and CEO of Mainstreet