"Of course, that became 30-something years, as it turned out he was right about Khomeini, which he reminds us of all the time."
While his parents purposefully distanced themselves from their homeland's traditional Islamic faith, Aslan briefly embraced evangelical Christianity as a 15-year-old after hearing the stories of the Gospel for the first time at a youth camp. Admitting that he now identifies himself as a Muslim "because the language of it makes most sense to me", he studied religion at Harvard Divinity School before becoming the University of Iowa's first full-time professor of Islam in 2000.
"I suppose you could say it was a form of teenage rebellion," he laughs. "My father would say he was flabbergasted that I was going to study religion for a profession. Iranian immigrants to the US either become lawyers, doctors or engineers and I guess he assumed I would take up one of those fields. I also should say he was always unconditionally supportive about the things I've done and was obviously very proud of the success I have achieved."
Aslan first rose to prominence after the publication of his 2006 book No God But God, an Islamic history from a liberal viewpoint. Lambasted by critics for apparently dumbing down his rarefied subject matter, he has always aimed to appeal to a wide audience.
"I've been called unserious, an amateur and a dilettante," he says. "Not because they question my credentials but because of my insistence on simplifying these issues and making them accessible to a general audience, which is often frowned upon in academia."
Styling Zealot as a biography of Christ, he hopes it shows a personal side to the Jewish preacher-turned-Messiah's character. "When you write about Jesus, it's difficult to separate him as a historical figure from the Christological ideas that have arisen around him," he explains. "I wanted to make it absolutely clear to the reader that this is not a book about Christianity because Jesus was not a Christian, he was a Jew. This is a book about a man who lived 2000 years ago in a land the Romans designated Palestine, a man who confronted very specific social ills and a very specific set of religious powers. So his teachings and actions have to be understood exclusively within the framework of the world and time in which he lived."
Aslan believes it is the book's down-to-earth approach that has struck a chord with so many people. "It's partly to do with how the core of Christianity is that Jesus is both God and man," he says. "But the man part of his identity gets subsumed in church as you mostly hear about the God part of him. Even when you do hear about Jesus as a man, there is a kind of safety net to some of the stories. After all, no matter how difficult his trials and tribulations were, in the end he is still God and that therefore provides a little bit of an out for some of the things he does. But when you read about Jesus purely as a man living in a particular time and place, the struggles he faced and the powers he confronted become a lot more real."
However, Aslan admits that Zealot makes for an emotionally loaded title in this day and age.
"The word has a different connotation today than it did in Jesus' time, when zealotry was a widespread phenomenon," he says. "Most Jews would have proudly referred to themselves as zealous to the Lord. Indeed, zeal is an actual biblical doctrine referenced in the Hebrew Bible. It relates to a belief in the sole sovereignty of God and a refusal to serve any master, human or not, except God. All the great biblical heroes - the great kings and prophets of old - were known for their zeal and in Jesus' time being zealous was a point of pride."
Zealot (Allen and Unwin $36.99) is out now.