The Indianapolis Star talked to Batman Begins director Christopher Nolan about why they cast Liam Neeson in the role of Henri Ducard:
“We were looking for someone to play a mentor that the audience would immediately warm to and see as trustworthy,” says director Christopher Nolan (“Memento”). “The baggage Liam carries is very useful. He presents a seductive quality that is very important in bringing Bruce Wayne into his point of view.”
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Source: Indianapolis Star