Originally Posted by Daryl
Katie Holmes wasn't Christopher Nolan's choice; she was imposed on him by the studio from the get go. WB had found out that a demographic remained impervious to these superhero films: teenage girls. Therefore they tried to lure this audience by casting an actress which starred in a popular teen TV series (Dawson's Creek).
That's not strictly true. Nolan wrote the part for Holmes. They'd known each other since 2001 when Nolan was prepping Insomnia (their offices at WB were on the same lot), and he believed that she had the warm girl-next-door vibe he was aiming for with Rachel. I think he was right. So yeah, he was encouraged to write a female love interest by the studio, but he always wrote it with Holmes in mind. Nolan and his wife actually remain good friends with her post-Begins and attended her wedding in Italy (along with Bale and Caine).