Scott Matthews was an astronaut and one of the first humans who were captured by the aliens. Matthews submitted to them and accepted the Leech inside him, becoming one with it like Ryan Lainus did later.
When the aliens arrived on earth, he was the one to address to the humans and offer the plan to surrender. He then stayed inn the white house, demanding the best of the accomodations, as if something happened to him the aliens would attack, and when the humans rejected the offer he was killed, despite the long tradition that messengers are to remain unharmed