Alpha is the remains of a V which was found on Earth long before the V's arrival.
Alpha had been on Earth for 50 years. Alpha was discovered in a crater with other bodies which were human. Tests were taken, and it known that Alpha came from space.
It was Alpha which lead to the reveal of Red Sky's true purpose: to change Earth to an V environment.
Alpha skeleton shows us underneath the scales of the V's. They have two big eye sockets with a hole in the middle which is meant to be the nose. They show the reptilian teeth. It also shows the tail, the arms, the legs and a rib cage which has lost a majority of it.