When U.S. officials join talks this weekend about Iran's nuclear program, they will be armed with profiles developed by intelligence agencies offering insight into what makes foreign leaders tick.
One key player will not be at the table in Istanbul, where negotiations are scheduled between Iran and six world powers, but his stamp of approval will be required for any deal to fly.
"Iran's supreme leader, Ali Khamenei, has the final word on Iran's foreign, domestic, and security policies. He is the ultimate decision-maker," a U.S. official said.
Since U.S. severed diplomatic ties more than 30 years ago, first-hand observation of Iranian leaders is a rarity for Americans. U.S. spy agencies must rely on the inexact art of long-distance analysis to profile leaders of an opaque system.
Former U.S. officials and Iran experts say Khamenei has a deep-rooted suspicion of the West and a streak of insecurity - he rose to power due to his loyalty to the late Ayatollah Ruhollah Khomeini rather than lofty religious credentials.
A sense of inferiority has dogged him over the years and it would be especially important for Khamenei to be seen as not folding under Western pressure to reach an agreement, they said.
"There were many much more educated than he and he had to prove himself in a continuing fashion to those who considered his credentials inferior," said Jerrold Post, director of the political psychology program at George Washington University.
"He has always been a balancer. Taking competing interests and finding a way of weighing them both, which is positive in some ways but also can at times give a sense of vacillation," said Post, a doctor who founded the CIA's Center for the Analysis of Personality and Political Behavior.
The functions of that center are now in a CIA unit called the Medical and Psychological Analysis Center, where doctors and psychologists produce physical health and psychological profiles of foreign leaders.
Other leadership analysts in the CIA's Directorate of Intelligence, with degrees in political science, international relations, anthropology and political psychology, also profile foreign leaders and decision-makers to help U.S. policymakers deal with their counterparts.
The practice of compiling psychological profiles of foreign leaders from afar has engendered occasional scepticism.
One substantive criticism, a former intelligence official said, is that the profiles sometimes are so general in describing a leader's personality that they are of little help to decision-makers. There is also a "so what" element to knowing a leader's psychology because U.S. officials must react to their actions rather than personality, another former official said.