Ira Winkler
Former NSA analyst who built a career on showing how easily companies fool themselves.
After leaving the NSA, Winkler ran penetration tests in which the main tool wasn't code but a telephone and a plausible story. Using social engineering he talked his way into companies and walked out with sensitive information within days, then wrote it up. Corporate Espionage (1997) and Spies Among Us (2005) describe how industrial espionage really works: rarely with sophisticated tools, usually with someone asking nicely.
Later he turned largely to security awareness, arguing that user error should be treated as a system failure to be engineered away rather than blamed on a "stupid user". It's a message well suited to the age of phishing.