Guthix originally created the world of RuneScape and went into a deep "sleep". This is when the God wars occurred and Saradomin and Zamorak usurped the world of Guthix. They would have continued to battle had Guthix not reawakened and made them stop.
Guthix calls the world in which RuneScape is set "Gielinor", claiming it as the name he christened it with in the beginning. Guthix is often seen as a floating head with tendrils attached to it but can appear in multiple forms. His true form is impossible to comprehend by mortals. His followers are limited but include the druids and gnomes. The dwarfs, though not particularly religious, respect Guthix as the source of the metals they mine so diligently. The unique trait about Guthix is that, unlike Zamorak and Saradomin, he does not need followers to remain on the mortal realm but instead draws strength from all living things, showing why he does not demand worship from those who follow his ways.