After chasing hackers for the Air Force, building AOL’s incident-response muscle and riding Mandiant into a billion-dollar deal, ‘Merk’ was finished with security startups. A complaint about lousy service changed his mind - and became the premise for Expel.

After a career that runs from the Marine Corps to Harvard and through some of cybersecurity’s best-known companies, eSentire’s new CMO has a deceptively plain assignment: make a complicated defense business understandable.