King Abdullah II of Jordan, a member of the US-led coalition battling the Islamic State group, faces the toughest challenge of his 16-year reign after IS murdered a downed pilot.
One of Washington's closest allies in the region, Abdullah was catapulted into the forefront of the conflict with the jihadists after IS burned the captured Jordanian airman alive.
The British- and US-educated Abdullah became king in 1999 following the death of his father Hussein, a seasoned statesman who had weathered many challenges of his own.
On Wednesday, the day after IS released a video purporting to show F-16 pilot Maaz Kassasbeh being burned alive, Jordan executed two Iraqi jihadists, including would-be suicide bomber Sajida al-Rishawi.
She had been on death row for her role in 2005 triple hotel bombings in Jordan that killed 60 people, and the jihadists had demanded her release.
On Thursday, dozens of Jordanian warplanes raided IS targets, with the military vowing that the campaign to avenge Kassasbeh had just begun.
Analysts say Abdullah, who celebrated his 53rd birthday on January 30, was decisive in his response.
"King Abdullah is very realistic when faced with crises," said Mohammad Abu Rummaneh, a researcher at Jordan University Center for Strategic Studies.
Robert Danin, a senior fellow at the US-based Middle East Studies Council on Foreign Relations, agreed.
"King Abdullah has been clear-minded in seeing IS as a threat both to the kingdom and to the regional order in the Middle East," he said.
'Quick and decisive'
"King Abdullah was quick and decisive to act. First in ordering the execution of the two convicted terrorists, and then in intensifying the military campaign against IS," Danin said.
"This is important because it signals that the threat posed by IS is real and unacceptable."
Abdullah, a military man who was thrust into the limelight of politics following his father's death, cut short a visit to Washington and vowed a harsh revenge for the execution of Kassasbeh.
The king attended Britain's prestigious Sandhurst Military Academy like his father, earned his wings as a Cobra attack helicopter pilot and also commanded Jordan's Special Forces before becoming monarch.
He is married to Queen Rania, 44-year-old Kuwait-born Palestinian, an asset in a country where almost half the population of seven million is of Palestinian origin.
They have four children -- Crown Prince Hussein, Princesses Iman and Salma and Prince Hashem.
Jordan's constitution gives Abdullah extensive powers.
He appoints governments, approves legislation and can dissolve parliament. He has solid ties with tribes that form the backbone of the Hashemite kingdom.
Abdullah has described Jordan as a country wedged between "a rock and a hard place" -- a reference to its location between war-wracked Iraq and the Israeli-occupied West Bank.
'Delicate balancing act'
The war that has raged for nearly four years in neighbouring Syria has added to the challenges facing Jordan and the brutal rise of IS has put the country further on edge.
In September, Jordan joined the US-led coalition of Arab and Western countries, launching air strikes on jihadist targets in Syria where IS has set up a "caliphate" that also straddles areas it holds in Iraq.
Nadim Shehadi, director of the US-based Fares Centre for Eastern Mediterranean Studies, said "Daesh", the Arabic acronym for IS, poses a clear threat to both Jordan and coalition partner Saudi Arabia.
"One should not underestimate the danger that Daesh presents for both Jordan and Saudi Arabia as opposed to the danger it poses to Iran and (Syrian President Bashar al-) Assad," he said.
"For Iran and Assad, fighting Daesh gives them legitimacy and serves their interests; for Jordan and Saudi Arabia, fighting Daesh is a very delicate balancing act and one with potentially grave results.
"Daesh challenges them on their own ground, so Daesh is a much greater threat to them," he said.
Danin said the battle against IS was "thrust" on Jordan and other regional states, describing it as "a war of self-defence".
He also underlined the strength of US-Jordanian relations, noting that in just two months Abdullah had met President Barack Obama twice at the White House.
"It is clear that the United States is looking to Jordan as a model of stability and moderation in an extremely turbulent region," Danin said.