Apparently we have Joseph Gordon-Levitt to thank for Arthur's wardrobe in Inception:
You know, I gotta say when I first started working on Inception, some of the drawings they showed me of their ideas for that character was uh sort of schlubby, sort of like, well he’s the tech guy, he runs the machines, you know, so maybe he should be wearing some sneakers and a plaid shirt et cetera and I was like “No, no, no.” This guy is in charge of making sure everything goes right. The Cobb character that Leonardo DiCaprio played, he’s like the artist and this guy’s like the producer. So, uh, I thought of my friend Jared, who is a theatre producer by day and he’s a very spiffy dresser. And I was like, “No, I want tailored suits and I want to slick back my hair, I want this guy to seem like meticulous, like he pays very close attention to detail.”
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source *flails*