When the first Tahitian invader/ colonists arrived in Hawaii around 1250 AD there were two groups already here. These were Marquesians, and a small statured group, now called the Menehune that lived on Kauai.  (search: The Menehune Ditch of Kauai).  
These groups were killed and enslaved by the wave of invaders from Tahiti.
Of course, in the millions of years that these Islands have existed it would be silly to believe that even those folks were the first to ever arrive at these shores.  I'm sure that many a wayward sailor or fisherman blown off their course discovered these islands but simply stayed a while and continued on to return to were they came from.