The Grebulon Leader was not the original leader, but since his people lost all their memories, identities and agenda, they either elected a Leader or had him usurp the position. The Leader likes spending time manipulating Earth events and ruling the Solar System from planet Rupert.
The Grebulon Leader uses his manipulation and charisma to influence Tricia MacMillian into coming to planet Rupert and using astrology to carry out their new agenda. He is skilful enough that he doesn't reveal his true mission to Tricia. He is later revealed to be in league with the Vogons and is eager to blow up Earth for them. The Leader uses astrology knowledge to give Prostetnic Vogon Jeltz the signal to blow up Earth and this happens, and the Leader then grows suddenly bored, because "it was very much like the other months except there was nothing on the TV any more." So he puts on some light music instead.
- It is actually implied that the Leader and the Grebulons may not have lost their memories at all; but the Leader lied to Tricia about this so she would pity him and do his work for him.
- One of the astrology books the Leader uses to help him blow up Earth is You and Your Planets by the lustful Gail Andrews. She inadvertently is responsible for the Earth's destruction.