The new leader of Somalia's Al-Qaeda-linked Al-Shabaab rebels is thought to be a devout and ruthless hardliner who was one of the most trusted lieutenants of the group's late chief, according to experts and analysts.
Al-Shabaab acknowledged in a statement on Saturday that Ahmed Abdi Godane, it's previous leader, had been killed in a US air strike on Monday.
The Islamist group named Ahmad Umar, also known as Abu Ubaidah, as its new head.
Very little is known about Abu Ubaidah, and a senior Al-Shabaab official only described him as having been very close to Godane, a hardliner who had overseen the group's transformation from local insurgency to major regional guerrilla threat.
"Avenging the death of our scholars and leaders is a binding obligation on our shoulders that we will never relinquish nor forget no matter how long it takes," the Al-Shabaab statement said.
"By the permission of Allah, you will surely taste the bitter consequences of your actions," it added, while also renewing a pledge of allegiance to Al-Qaeda chief Ayman al-Zawahiri, Osama bin Laden's successor.
Sources close to Al-Shabaab said Abu Ubaidah was thought to have been involved in a major internal purge that took place last year, when Godane eliminated several key rivals including a commander thought to be his likely successor.
Abu Ubaidah is also thought to have had a hand in the last year's killing of Alabama-born Omar Hammami — better known as Al-Amriki or "the American" — who was one of the most prominent foreigners fighting in Somalia but who fell out with Godane.
According to an intelligence source, Abu Ubaidah is believed to have played a role in Al-Shabaab's most shadowy and feared wing, the clandestine internal secret service known as "Amniyat", which Godane set up to maintain discipline and expose rivals and informers.
The source said the new leader is thought to be in his early 40s and from the southern port town of Kismayu, which is currently held by Kenyan troops fighting with the African Union's Amisom force.
He also once served as Al-Shabaab's governor in the Bay and Bakool region.
However disinformation cannot be ruled out, another intelligence source said, explaining that the pressure of constant surveillance and drone strikes means Al-Shabaab may even have named a "ghost" or "given a pseudonym" as a deliberate tactic to protect their real hierarchy.
Godane himself took over the leadership of the Al-Shabaab in 2008 after then military leader Adan Hashi Ayro was killed by a US missile attack.