http://www.arabamericanmuseum.org/alfred.shaheen.fabric.to.fashion Alfred Shaheen - ok, so he didn't actually *invent* the Hawaiian shirt (they'd been around since the 1930s) but he popularized them, by starting his own textile-printing operation, inventing his own printing techniques and designing fabrics inspired by native Hawaiian textiles and Asian art.
The fact that Elvis wore his shirts didn't hurt either.