KABUL (Reuters) – Ahmad Wali Karzai, the younger half-brother of Afghan President Hamid Karzai and most powerful man in southern Afghanistan, was killed by a close associate on Tuesday.

His death leaves a dangerous power vacuum in southern Kandahar province, birthplace of the Taliban and focus of recent efforts by a surge of U.S. troops to turn the tide against the insurgency.

Below are questions and answers about Ahmad Wali Karzai and his role in southern Afghanistan.

Q: WHY DID HE MATTER?

A: Ahmad Wali Karzai was arguably the most powerful man in southern Afghanistan, who acted as a regent and enforcer for his brother across the volatile region. His influence belied his modest official title, as head of the provincial council.

Critics said he was tainted by brutality and corruption that helped drive ordinary Afghans into the arms of insurgents. He was reported variously to have ties to the opium trade, private militias and the CIA — all charges he strongly denied.

But even enemies admitted he also brought a degree of ruthless control to a violent area through his unrivalled network of tribal and family connections and the personal fortune he was rumored to have amassed and used deftly for political ends.