The Golden One was one of the many Ewok gods; it had long been prophesied that he would one day appear to the Ewoks in person.
When C-3PO and his companions with the Alliance to Restore the Republic arrived on Endor in 4 ABY, the Ewoks took the gold-plated protocol droid for the Golden One.
The Ewoks of Bright Tree Village, under the leadership of Logray and Chief Chirpa, almost roasted Han Solo, Chewbacca, and Luke Skywalker at a banquet in C-3PO's honor. Before the fires could be lit, Luke Skywalker used telekinesis to lift the droid into the air (supposedly as a divine power of the Golden One) to scare their captors. As a result, the Ewoks freed the Rebels.
Later that night, C-3PO recounted the Galactic Civil War for the Ewoks, and translated his companions' pleas for help fighting the Galactic Empire. The Ewoks were convinced by Leia Organa's plea to the Ewoks to join in the fight and defend their trees. The Rebels were adopted into the Ewok tribe, and won the Battle of Endor thanks to Ewok assistance.
"The Golden One" was C-3PO's Basic translation of the name of the Ewok god rather than the Ewokese name.