In accordance with the post-a-day challenge by SunderedWorldDM, whose dreams bore the Orbseeker and whose deeds send the world shuddering.
From the AD&D Deities and Demigods section on ascending to godhood. "As study of the various mythologies will show, it is remotely possible for mortals to ascend into the ranks of the divine... the character in question must have advanced to an experience level that is significantly above and beyond the average level of adventure-type characters in the general campaign... For example, if the average level of characters in a campaign, both player and non-player, is around 5th level, then a candidate for ascension should be something like 9th or 10th level." The other requirements are to have their ability scores raised, a body of sincere worshipers, and faithfully following one's alignment.
From the AD&D Monster Manual. "Bandits will always be led by an 8th, 9th, or 10th level fighter..." Also "Berserkers will be led by a war chief of 9th or 10th level..." Also "Dervishes will be led by a cleric of 10th, 11th, or 12th level..."
If we assume that the average character in the setting is 5th level (which in fact seems very high to me), we might imagine a world in which leaders of relatively small groups have the potential to become gods. While assumptions like this don't necessarily follow from the gamey premises we cite here, I like the idea, and don't find it too silly. Plenty of mythic literature suggests that the baddest guy around might be looking for a way to finally become powerful enough to start a priesthood dedicated to his own magnificence. If we compare Deities and Demigods's stats for, say, Sir Launcelot (Paladin 20 that he is), we can imagine a twist on Arthurian literature in which rather than fleeing to France he simply deigns to rule England as its god-king, changing the tenor of the conflict somewhat.
In GLoG, we don't have such high levels, and don't rely on the minutiae of AD&D texts anyway, but the attainability of immortality is a worthy characteristic of any setting in which characters gambling so much to make their names. To put some kind of crunch on it, we may say that anyone of 3rd level or higher, who somehow gets at least one ideal to 19 or higher, and who has a body of sincere worshipers can ascend to the ranks of the divine.