Deities of Norrath

You select a deity when you create your character. If you are of a religious class (such as a cleric, shaman, etc.), selecting a deity is mandatory. However, if you are of a non-religious class, you may have the choice to be agnostic.
In either case, your religious choice is rather important, as it is is both permanent and plays a major role in affecting your character's faction standing. In other words, you cannot change your deity once your character has been created, and it in part determines which NPCs and factions will look amiably upon you, and which will dislike or even hate you. For example, choosing Innoruuk, the Prince of Hate, will undoubtedly make your character unpopular around the Temple of Rodcet Nife, the Prime Healer.
Keep in mind, however, that deity selection will not, in of itself, overcome racial hatreds - for instance, being a human worshipping Innoruuk will not make you welcome in Neriak, home of the Dark Elves.