BAGHDAD — Tariq Aziz, the debonair Iraqi diplomat who made his name by staunchly defending Saddam Hussein to the world during three wars and was later sentenced to death as part of the regime that killed hundreds of thousands of its own people, has died in a hospital in southern Iraq, officials said. Aziz died Friday of a heart attack after he was taken to the al-Hussein hospital in the city of Nasiriyah, about 200 miles southeast of Baghdad, according to the provincial governor, Yahya al-Nassiri. The only Christian among Hussein’s inner circle, Aziz’s religion rescued him from the hangman’s noose that was the fate of other members of the top regime leadership. Iraq’s president at the time, Jalal Talabani, then refused to give the death sentence his required signature, citing Aziz’s age and religion. A skilled operator in the halls of the United Nations, he was the government’s front-man in dealing with U.N.