A few nights after he resigned his post as secretary of state two years ago, Colin L. Powell answered a ring at his front door. Standing outside was Prince Bandar, then Saudi Arabia’s ambassador to the United States, with a 1995 Jaguar. Mr. Powell’s wife, Alma, had once mentioned that she missed their 1995 Jaguar, which she and her husband had traded in. Prince Bandar had filed that information away, and presented the Powells that night with an identical, 10-year-old model. The Powells kept the car  a gift that the State Department said was legal  but recently traded it away.

The move was classic Bandar, who has been referred to as Bandar Bush, attending birthday celebrations, sending notes in times of personal crisis and entertaining the Bushes or top administration officials at sumptuous dinner parties at Prince Bandar’s opulent homes in McLean, Va., and Aspen, Colo.

He has invited top officials to pizza and movies out at a mall in suburban Virginia  and then rented out the movie theater (candy served chair-side, in a wagon) and the local Pizza Hut so he and his guests could enjoy themselves in solitude. He is said to feel a strong sense of loyalty toward Mr. Bush’s father dating to the Persian Gulf war, which transferred to the son, whom he counseled about international diplomacy during Mr. Bush’s first campaign for president.

After the Sept. 11 attacks, as the United States learned that 15 of the 19 hijackers were Saudi and focused on the strict Wahhabi school of Islam that informed them and their leader and fellow Saudi, Osama bin Laden, Prince Bandar took a public role in assuring the Americans that his nation would cooperate in investigating and combating anti-American terrorism. He also helped arrange for more than a hundred members of the bin Laden family to be flown out of the United States.

Even since he left the Saudi ambassador’s post in Washington and returned to Saudi Arabia two years ago, Prince Bandar has continued his long courtship, over decades, of the Bush family and Vice President Dick Cheney, flying into Washington for unofficial meetings at the White House. He cruises in without consulting the Saudi Embassy in Washington, where miffed officials have sometimes said they had no idea that he was in town  a perceived slight that contributed to the resignation of his cousin Prince Turki al-Faisal as ambassador to the United States last year. He has been succeeded by Adel al-Jubeir, who is said to have strong support from the king.

Prince Turki was never able to match the role of Prince Bandar, whom the president, vice president and other officials regularly consult on every major Middle East initiative  from the approach to Iran to the Israeli-Palestinian peace process to Iraq. Prince Bandar played a crucial role in securing the use of the Prince Sultan Air Base at Al Kharj, roughly 70 miles outside Riyadh, in the attacks led by the United States against Afghanistan and Iraq, despite chafing within his government.

He helped in the negotiations that led to Libya giving up its weapons programs, a victory for Mr. Bush. He pledged to protect the world economy from oil shocks after the invasion, the White House said in 2004, but he denied a report, by the author Bob Woodward, that he had promised to stabilize oil prices in time for Mr. Bush’s re-election campaign.