The first military encounter in which our hero showed his genius was the Battle of Uhud, which he while a polytheist caused to be the worst for Muslims in the early days of Islam.
His father was the local equivalent of a judge and ruled on matters brought before him.
What am I waiting for? Several years earlier, in 632, Abu Bakr died and Omar became the new Caliphate.
At first Khalid complained about 'Umar's decision to companions.