The 28-year period from 1933-1961, bracketed on one end by Hitler's rise to power in Germany and on the other by the very height of the Cold War, was marked by a remarkably stable succession of American presidents. In fact, only three men held office in this period, and that predictability led to a general stability among government agencies. Conversely, the CIA had five different directors in its first 15 years, from 1946-1961, and then nine different directors in the next 20, with four of those directors serving less than a year. But of all the CIA's directors, none wielded the immense influence or power of Allen Dulles, who, together with his brother, Secretary of State John Foster Dulles, became arguably the two most powerful people in the government after the president. 

To this day, Dulles' eight-year tenure in that office is the longest, and as one of the country's leading experts in international law, intelligence, and spycraft, he became renowned for his unwavering anti-communist ideology and readiness to take decisive measures to counter what he perceived as a menace to American safety. As such, it would be Dulles who sanctioned many of the CIA's most notorious operations, including the ousting of Iran's democratically elected government in 1953, spying and experimentation on American citizens, and the disastrous Bay of Pigs. That last episode cost him his job, though he continued to play a role in American political life after President John F. Kennedy forced him out of the CIA in 1961. 

By then, however, Dulles had already had an outsized influence on the direction of the country, and to this day his legacy can be felt, even as his reputation continues to be a source of much debate.