Majid Khademi, the IRGC intelligence chief killed in Tehran early Monday, was not a battlefield commander so much as a career security insider who rose through Iran’s secretive counterintelligence system and helped oversee repression, surveillance and anti-infiltration work. His death matters because he sat at the junction of two of the system’s most sensitive functions: guarding the Guards from infiltration and directing the intelligence arm accused of crushing dissent. In March, Washington’s Rewards for Justice program offered up to $10 million for information on Khademi and other senior IRGC figures, a sign that he was seen abroad not just as...