Sienna Miller most definitley. Somew ill say Kate Moss, but people - Sienna is the one that's in EVERY magazine and famous for her style, before I came here to this board - I honestly haven't heard much about Moss' style, whether she had it first or not. Sienna made it public, everyone wanted to dress like her this year, she was hyped as the new style icon,etc... It was like nothing I've ever seen before.
I love Jens style, but nowhere did she 'define' 2005 with it. Stella McCartney..same thing as with Moss, she has a popular style in the fashionindustrie, but for the broad mass - no.
So Sienna most definitley. She came 2005 and is super famous for her style and copied by millions.