Abid Hamid Mahmud al-Tikriti had been in custody since 2003, CNN reported. He was the ace of diamonds in the U.S. military's symbolic deck of cards of leading Iraqis, with only Hussein and his two sons ranking higher.
Al-Tikriti, who was sentenced to death by the high tribunal for genocide, was an important member of Saddam's inner circle. He served as national security adviser and head bodyguard as well as secretary.
He was arrested by U.S. Special Forces near Tikrit in 2003, not long after the invasion.
Saddam was hanged in December 2006. His sons, Uday and Qusay, and Qusay's 14-year-old son were killed in 2003 after U.S. forces got a tip they were staying in a villa in Mosul.
Interpol investigating stolen passports on missing flight
Senate Democrats to pull all-nighter on climate change