James Comey's firing was a shock—but not entirely unprecedented. Since its founding in 1908, the FBI has been led by 11 men (interspersed with a handful of acting directors), and Comey was the second of them to be fired. William Sessions got the boot in July 1993 compliments of Bill Clinton, though in that case, Sessions had been asked to step down and only saw his position terminated once he refused. The Los Angeles Times reports the Justice Department's Office of Professional Responsibility began looking into the Ronald Reagan appointee at the end of George H.W. Bush's tenure and uncovered a rash of ethical transgressions that were detailed in a report released in January 1993.
Among them, per the Times and New York Times: Having a $10,000 security fence constructed around his home that didn't actually provide security, flying free on FBI aircraft in order to meet relatives, and sidestepping taxes owed on his use of an FBI limo. Attorney General Janet Reno determined "in no uncertain terms that [Sessions] can no longer effectively lead the bureau" and recommended Clinton fire him. The Washington Post reports two presidents—Truman and Kennedy—considered firing J. Edgar Hoover, who held the post for nearly 48 years and whose political clout allowed him to escape such a dismissal. Ten-year term limits were established after Hoover's death. Sessions was six years into his term; Comey was only three. (When Comey first heard the news he thought it was a joke.)