John Kerry seized the reins of US diplomacy on Monday, winning a warm welcome from State Department staff as he took over from Hillary Clinton in what he described as a "homecoming."
Proving that "the Foreign Service is in my genes," Kerry brandished a battered copy of his first diplomatic passport, issued at the age of 11 when his diplomat father was posted to Berlin.
And he triggered laughter from hundreds packed into the bureau's grand entrance when he mused "Can a man actually run the State Department?" before admitting with some self-deprecating humor: "I have big heels to fill."
The new secretary of state paid tribute to Clinton, who followed Condoleezza Rice into the job and stepped down on Friday after four years in office.
"Job well done. The nation is grateful. The world is grateful. Thank you, Hillary Clinton, and thank you, her team," Kerry said.
He later wrote on the official State Department blog about "a day of milestones," saying that "in more ways than one, it's a homecoming."
Following a round of weekend phone calls with some world leaders, Kerry on Monday spoke with British Foreign Secretary William Hague, as well as his French and German counterparts Laurent Fabius and Guido Westerwelle.
"You can imagine that this is a week of introductions, or at least an initial few days of introductions," State Department spokeswoman Victoria Nuland said.
The former Massachusetts senator already has a myriad of problems spilling out of his inbox.
After the recent losses of American diplomats, killed in an assault by militants on the US mission in Benghazi, Libya, Kerry promised to make the security of the department's 70,000 diplomatic staff his top focus.
He told the staff who turned out to greet them that he understood "how critical it is that you have somebody there advocating for you. The dangers could not be more clear."
He vowed he would honor the deaths of ambassador Chris Stevens and the other Americans who died in the September 11 attack in Benghazi.
"I pledge to you this: I will not let their patriotism and their bravery be obscured by politics, number one," he said.
"Number two, I guarantee you that, beginning this morning, when I report for duty upstairs, everything I do will be focused on the security and safety of our people."
Kerry, a long-time member of the Senate Foreign Relations Committee, was sworn in on Friday and has already spoken with many leaders, including those in traditional North American allies Canada and Mexico.
But perhaps the most interesting calls were to Israeli President Shimon Peres on Saturday, and Israeli Prime Minister Benjamin Netanyahu and Palestinian president Mahmud Abbas on Sunday.
During his confirmation hearings last month, Kerry hinted he may have some ideas for rekindling the moribund Israeli-Palestinian peace process, and it is thought he may stop in the region for his first foreign trip later this month.
On Monday, though, he was quick to show off his credentials for the job of steering American diplomacy in a world forever changed by the uprisings which swept the Arab world and North Africa two years ago.
He took from his pocket his boyhood green diplomatic passport. The first stamp dates back to 1954 from the French port of Le Havre, when after six days at sea, the Kerry family arrived in Europe on their way to Berlin.
Kerry, 69, revealed how he learnt his first lessons about "the virtue of freedom" during bicycle trips around the eastern, Russian-held sector of the divided German city in the wake of World War II.
The new secretary of state also took to Twitter on his first day, as officials revealed that the tweets Kerry directly writes on the @StateDept account would bear his initials "JK."
"Exhilarating to walk into @StateDept today and get to work with remarkable team. Dad on mind! -JK," Kerry wrote in his first personal tweet.
He also joked on Monday that he would be touring the building, and could look a little lost. And indeed he popped into a concert being given by the Afghanistan National Institute of Music.
"Music is the international language of peace and possibilities and dreams," he told the young players, winning applause when he said that as a young man he had played in a rock band.
"I still play guitar. When I go home, I love to play guitar," he revealed.