Soft-spoken and slight, Adel al-Jubeir’s low-key presence as Saudi Arabia’s ambassador to Washington belies his powerful position as chief foreign policy adviser to Saudi King Abdullah.

Although Jubeir has amassed a wealth of contacts during his decades on and off in the United States, his access to the ear of the king, his ability to speak directly for the monarch and his chair at Abdullah’s side during virtually every high-level contact with world powers have given him a stature few diplomats can claim.

But Jubeir is not a member of the Saudi royal family, and despite long-running tensions between the governments in Tehran and Riyadh, it remains unclear what Iran’s purpose would be in targeting him for assassination in the U.S. capital as the central element of the plot alleged Tuesday by Attorney General Eric H. Holder Jr.

Jubeir, 49, the son of a Saudi diplomat who speaks fluent German and virtually unaccented American English, is a political science and economics graduate of the University of North Texas and holds a master’s degree in international relations from Georgetown University.

As his government’s diplomatic point man in Washington, he has operated largely behind the scenes. Beyond his frequent meetings at the White House and the Saudi Embassy across the street from the Kennedy Center, invitations are highly sought to his private dinners at the embassy residence in McLean and quiet lunches at Georgetown restaurants, where his name is known and his favorite table reserved.

At other times in his career, Jubeir has been much more prominent. He first appeared as a spokesman for the Saudi government during the 1991 Persian Gulf War, following that assignment as a member of the Saudi delegations to the Madrid peace talks on the Palestinian-Israeli conflict and at international arms-control talks in Washington. During the mid-1990s, he was part of the Saudi delegation to the United Nations and spent a year as a diplomatic fellow at the New York-based Council on Foreign Relations.

In 2000, he served briefly as director of the Saudi Information Office at the embassy in Washington — a position now held by his brother, Nail — before officially becoming an adviser to Abdullah.

When it became known that 15 of the 19 hijackers in the Sept. 11, 2001, attacks were Saudi citizens, Jubeir was dispatched to the United States to represent the kingdom’s interests before policymakers and the American public. His public prominence overtook that of the then-ambassador, Bandar bin Sultan, as the Saudis struggled to present the kingdom as a U.S. friend in the Middle East.

In the days after the al-Qaeda attacks, he was a ubiquitous presence in U.S. news reports, unfailingly reasonable and well-spoken as he calmly parried questions about everything from whether Saudi Arabia could be trusted as a counterterrorism partner to why women are not allowed to drive in the kingdom. In private, he often counsels patience in defending the royal family’s slow and sometimes halting process toward civil and political rights and gender equality.

Since becoming ambassador in early 2007, Jubeir has frequently traveled outside the country, going regularly to Riyadh and accompanying Abdullah on state visits around the world.

Despite his sophisticated smoothness, Jubeir can be bitingly curt in representing his government. In an April 2008 meeting with the U.S. Embassy’s charge d’affairs in Riyadh, he reminded the Americans of “the king’s frequent exhortations to the U.S. to attack Iran and so put an end to its nuclear weapons program,” the embassy reported in a State Department cable released by WikiLeaks.

“  ‘He told you to cut off the head of the snake,’ ” the charge d’affaires reported Jubeir as saying of Abdullah, and noted that rolling back Iranian influence in the region was “a strategic priority for the king and his government.”