UNITED NATIONS , United States - Antonio Guterres assumes the reins of the United Nations on Sunday hoping to breathe new life into the world body, in the wake of its impotence over Syria's humanitarian catastrophe.
The Portuguese former prime minister, 67, will become the first onetime head of government to lead the UN, succeeding South Korea's Ban Ki-moon for a five-year term.
His unanimous election has energised UN diplomats who see him as a skilled politician who may be able to overcome the divisions crippling the United Nations.
One Western ambassador regretted only that a woman wasn't picked to take the post for the first time, adding with a smile that "except for the gender, he is perfect." Guterres faces a monumental task grappling with complex crises in Syria, South Sudan, Yemen, Burundi, North Korea and elsewhere - overseeing a clunky entrenched bureaucracy and a bitterly divided Security Council that will leave him little room to manoeuvre.
Donald Trump's arrival in the White House on January 20 likely will further complicate his task.
Guterres has acknowledged that "the secretary general is not the leader of the world," but rather that his work depends on the goodwill of the world's great powers.
After two terms under Ban, widely criticised for lacking initiative and charisma, some diplomats are banking on a change of style and personality to revitalise the UN.
An engineer by training and a practising Catholic, Guterres fought for migrants' rights as the UN High Commissioner for Refugees from June 2005 to December 2015.
He served as prime minister of Portugal from 1995 to 2002, anchoring his country to the European Union and working to raise living standards.
He has laid out three priorities for change: working for peace, supporting sustainable development and improving internal UN management.
One issue looms above the others, however.
"My deepest regret on leaving office is the continuing nightmare in Syria," Ban recently declared.
The UN has looked on helplessly as the Syrian army laid siege to the rebel stronghold of Aleppo, the country's second city, backed by Russia and Iran.
Their sole concession to the UN was to allow a small handful of observers to follow the evacuation of thousands of civilians.
"Too little, too late," one diplomat said.
During almost six years of war, Russia has protected its Syrian ally from Western pressure by using its veto in the Security Council to torpedo resolutions over the conflict six times.
Guterres inherits the portfolio with Moscow and Ankara spearheading a nationwide ceasefire effort.
Russia is pushing a political solution to the crisis that would hugely favour Syrian President Bashar al-Assad, reinforced by his conquest of Aleppo.
Western diplomats believe the incoming UN chief should put his own ideas on a settlement forward fairly quickly, without binding himself to any formal peace plan.
For the time being, "he is keeping his cards close to the chest," another diplomat said.
Vowing to "engage personally" in conflict resolution, Guterres has remained vague about his plans.
"We need more, mediation, arbitration and preventive diplomacy," he has said.
However, Ban has already gone through two Syria mediators - Kofi Annan and Lakhdar Brahimi, who both resigned - before appointing Staffan de Mistura, who has appeared exasperated over the UN's powerlessness over the conflict.
The same helplessness and at times disunity has marked the UN's response to the civil war that ravaged South Sudan for three years. A US initiative to impose an arms embargo failed, winning only seven votes from the 15 countries that sit on the Security Council.
The approximately 13,000 peacekeepers deployed in the country have been criticised for failing to protect the civilians crowding UN bases.
Elsewhere on the continent, accusations of rape have permanently tarnished the reputation of UN peacekeepers in the Central African Republic.
Guterres has acknowledged the criticism, saying "it is time for the United Nations to recognise its shortcomings and to reform the way it works." "The United Nations needs to be nimble, efficient and effective." He has already begun implementing one of his promises - working toward gender parity - by appointing three women from developing countries to key positions, including Nigeria's Environment Minister Amina Mohammed as deputy secretary general.
The main unknown is the impact Trump's presidency will have on the UN and global affairs.
The Republican billionaire has shown mistrust and even a degree of contempt toward the United Nations and threatened to revisit the Paris climate change agreement, one of Ban's biggest successes.
That has caused concern, given he is the future leader of the UN's main donor, which contributes 22 per cent of its budget.
It's also unclear what effect a US-Russia rapprochement - something Trump advocates - would have on the Security Council.
Last week, Trump sought in vain to prevent the council from adopting a resolution denouncing Israeli settlement building in the West Bank, after which he tweeted: "As to the UN, things will be different after Jan. 20th."