He initially lived in somalia then Came to Kenya
He lived in Alabama US
The rapping American
Omar Hammami, alias Abu Mansoor al-Amriki, was an al-Shabab poster boy, but many thought he had outgrown his shoes - a term used in Somalia to describe individuals with raised self-importance.
An Alabama native with a $5m FBI bounty on his head, Hammami had criticised the leader, Godane, before seeking refuge in the jungle of Bay and Bakool.
The fallout was well publicised.
The American, who was known for his rapping skills, thought he would be safe in Omar's backyard - a fatal error of judgment.
Under orders from Godane, fighters loyal to Omar tracked the American down and killed him in a hail of bullets.
With that move, Omar proved his loyalty to the cause and announced himself to everyone in style; he was to be taken seriously.
Living in Kenya
After the collapse of the Siad Barre regime in 1991, Omar, like hundreds of thousands of other Somalis, had crossed the border into Kenya.
He lived there for several years and learned the language, sources close to him have told me, adding that Omar knows Kenya like the back of his hand.
READ MORE: Al-Shabab claims deadly Kenya attack
Like other senior operatives of the group, his aides told me, he is not just driven by ideology but also by bad experiences while living in East Africa's biggest economic power.
Attacking Kenya is his pet project; daring hours-long sieges are his way of grabbing people's attention, while foot soldiers with AK-47s are his preferred mode of communication.
Bloody beginning
In his first six months in charge, more Kenyans died in al-Shabab attacks than during Godane's three-and-half-year reign.
Shedding the blood of his perceived enemies in Kenya is what drives him, his close associates told me.
He, like most leaders of the group, knows he will likely have a short lifespan.
WATCH: Kenya's Enemy Within
They are constantly on the move to evade being tracked down by drones, so they spend their time thinking of ways to reach paradise with the blood of their enemies.
For the last two years of the former emir's reign, Omar was responsible for al-Shabab's footsoldiers. It is reported that he established at least one battalion of Kenyan-only fighters.
The idea is that many of these Kenyan al-Shabab fighters will later return to Kenya and wreak havoc in the coastal region, bringing the thriving tourism industry to its knees.
Counting war spoils
Unlike Godane, who only called for Kenyan troops to withdraw from Somalia, Omar is known for having bigger war plans and political appetites.