He wants to kill you.
Nothing personal, he wants to kill everyone. You are just the closest.
Something went very wrong on the day this construct was built. Very wrong, something involving fire and darkness, something violent enough to kill everyone present and damage the Forge itself. The only clue: a single word, painted on the Forge floor in blood – “DAVROSS” – and this newly-formed warforged, muttering “Exterminate! Exterminate!” over and over in a warbly high-pitched metallic voice.
With no better idea of what to do, the Cannith technicians who uncovered the mess sold the construct on the open market, crossing their fingers in the hope that nothing bad would result.