Galactus is a planet eater.. he devours planets... Surfer was
Norrin Radd, an astronomer of the planet Zenn-La.. when Galactus
came to Zenn-La, Radd saw Galactus first and to save his planet, he
made a pact with Galactus to serve as his herald.. to search for
other planets for Galactus to consume..
to save his planet, he had to leave his love and his home forever..
which is why the melancholic mood of the Surfer
Radd was given a bit of the Power Cosmic which is the power of
Galactus.. that power gave him the silvery sheen and enabled him to
command a board which he rides around the universe..
when Surfer came to Earth, he came into contact with the Fantastic
Four.. who reminded him of what it meant to be noble, to be
honourable..
Surfer then abandoned Galactus and was exiled to spend eternity on
Earth...
there.. in a nutshell 
