The Harvester was a massive machine on early-Earth controlled by The Fallen.
The Harvestor is an ancient machine used by the Primes to harvest Energon from nearby suns. The Primes had one rule; if the planet with a sun had life on it, it was not to be harvested. One of the Primes, The Fallen, tried to break this law by harvesting Energon from the Earth's sun. The Primes found out about this, and hid the Harvestor on the Earth, and hiding the Matrix of Leadership, the key to activating it.