The self-styled moderate, tasked with easing concerns over Iran's nuclear program, made history by speaking to US President Barack Obama in the first contact between the countries' leaders since the 1979 Islamic revolution.
Hassan Rouhani stole the show at the annual UN General Assembly summit, addressing nearly a dozen packed audiences or interviews in which he calmly, and with a smile, explained how he wanted better relations with the West.
A Twitter account in English tracked Rouhani's movements from a shot of him serenely sitting in a car Monday on his way in from the airport, to a shot of the white-turbaned cleric grinning broadly Friday as he boarded his plane home.
The shift could not be more stark from his predecessor Mahmoud Ahmadinejad, who was also fond of appearances overseas but was greeted with walkouts, protesters and diplomatic rebukes for his bombastic defense of Iran's nuclear program and his denial of the Holocaust.
Rouhani, who understands English but almost exclusively spoke Farsi in public, condemned the Holocaust in the face of repeated questions, while also diligently criticizing Israel.
Critics, notably Israeli Prime Minister Benjamin Netanyahu, accused Rouhani of offering little different from Ahmadinejad other than a more elegant delivery, and charge that Iran is seeking nuclear weapons.
But most foreign leaders who met Rouhani said they were impressed, or at least hopeful, that he can find a peaceful resolution to a row that until recently had prompted talk of a US or Israeli attack.
"My frank impression of President Rouhani was that he is willing to fully cooperate with the international community," said Prime Minister Shinzo Abe of Japan, which historically has had cordial relations with Iran.
French Foreign Minister Laurent Fabius, who accompanied President Francois Hollande in a meeting with Rouhani, praised the "week of the thaw."
"There is a very, very sharp change in attitude from the Iranians. That's something positive. Now we need to see how to translate that into facts," Fabius said.
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In a telephone call that would have been unthinkable weeks ago, Rouhani spoke for 15 minutes by telephone with Obama, who signed off by telling him goodbye -- "khodahafez" -- in Farsi.
Obama reached out to Iran after entering the White House in 2009, but said he was disappointed by the lack of reciprocation.
After appeals from Israel and US lawmakers, the Obama administration spearheaded tough sanctions on Iran's oil and banking sectors. The measures have wreaked havoc on Iran's economy, and the Tehran leadership eagerly want them lifted.
Alireza Nader, senior international policy analyst at the Rand Corp., said that Rouhani, who studied in Scotland, and his US-educated Foreign Minister Mohammad Javad Zarif knew how to relate to the West.
"He gets it. He gets what the US is concerned about and he knows how to put on the charm," Nader said of Rouhani.
"He's showing a side that I think a lot of Americans in the foreign policy community wanted to see, so that's why you get a lot of excitement," Nader said.
While warning that diplomacy may prove difficult, Nader said that Rouhani's UN performance -- and talks with Obama -- showed that he enjoyed the backing of Iran's supreme leader Ayatollah Ali Khamenei.
Mark Dubowitz, executive director of the Foundation for Defense of Democracies, a US group which advocates a hard line on Iran, agreed that Rouhani had shored up support in Tehran but said he saw little substantively different from Ahmadinejad.
"From Rouhani's perspective, his week was a smashing success and Rouhani-phoria is now at a feverish pitch," he said.
But he predicted the buzz would fade, and noted that Netanyahu -- who has branded Rouhani a "wolf in sheep's clothing" -- will meet Obama at the White House on Monday.
"Everybody has to get away from the euphoria of personality and to the more mundane task of nuclear physics," Dubowitz said.