The Pope, because if the aliens start saying they'll conquer us and aythang, he'll let 'em know we have a Super Being on our side. Where's your god now, aliens?!
Barack Obama, because the aliens will be shocked silly by the fact that Obama has overseen drone wars, executions, and such...and he won a peace prize! We're too dangerous to mess with.
OK, maybe Taylor Swift too, because it would be cool to see aliens dance to "Shake it off".