If you or someone you love has ever played a Cleric or a Paladin, then you know the moment: the time when you must Choose Your God. You can try to make one up out of thin air, or you can choose one from the setting. Unless you already have something in mind thin air can be tough, while the setting ones tend to be straightforward but not too compelling. "Minolalsa, Goddess of nature. Her symbol is a Tree. Borkorud, God of War. His symbol is a sword," and so forth. Gods like that are fine, of course, but tend to be forgettable; I've played many a game where the god barely comes up, and the cleric has to check his sheet to even remember what he's supposed to be worshiping. You can always go for the "I worship an ideal" option, but for my money if you're going to be running around quaffing mysterious potions and battling dragons and giants, you might as well go the whole nine yards and have the name of an incredibly powerful yet fickle being you can yell when things get crazy.
So with all that in mind, here's a God Maker table. It's a d20 four times,(one each for A, B, C, D) and by the end I'm hoping you'll have a deity whose name you'll be proud to invoke while bashing in someone's head with a mace. May also be useful for DM's who don't feel like coming up with a whole pantheon out of nowhere. The table will be followed by my long winded explanation.
All you need now is an impressive sounding name, and you should have "(Name) the (A), god of (B) and (C), whose followers wield the symbol of the (D)"
Now, the first thing you may notice is your god makes no sense.
That's OK, that's a good thing. Here, lemme introduce you to this fellow over here. His name is Apollo. He's the god of the Sun and Prophecy, and his symbol is a bow and arrows. This other fella, Poseidon, is the god of the ocean and horses, and his symbol is a fork. Thor over here is a weather god, his symbol is a hammer, and this Son of a Hebrew desert god has a Roman method of execution for his symbol.
Point is, making sense is not something actual religions strive for, at least not without the context of the stories involved. Actual religions are built up over time, with gods accruing additional "domains", names, and stories as the culture changes. In addition, they spread and move into other cultures, assimilating other gods as they go. Obviously one table isn't going to give you all this texture, so the idea is to make a jumping off point to get some texture by working backwards. It'll give him a title, a natural phenomenon, a cultural aspect, and a symbol.
For example, you roll the dice, you get Borkorud the Confined, god of Insects and Battle. His symbol is the Jug.
Why is he confined? Dunno. Maybe he was held prisoner by some other gods at some point in his history. Maybe he's an ascetic who confines himself to single spot due to some oath. Insects and Battle? Maybe it's a reference to flies and maggots on the corpses of a battle field, maybe it's the warrior-like nature of ants and wasps, or maybe he started out as the god of a very warlike tribe whose totem was a bee or something. It could just as easily have happened by accident, one tribe with a bee god unites with a tribe with a war god. The Jug? Maybe it's the carved out skull of an enemy god which he uses to drink the blood of the slain. Maybe there's a story where he had to lay siege to a fortress to retrieve a Jug with magical properties. Maybe he just likes to get drunk.
Basically, you roll the dice a few times, and then you try to make sense of it by contextualizing it. Now you've got a god with a bit of personality and the germs of a mythology. If you're making a few gods you can either re-roll repeats or scratch'em off and make up your own as you use them. The only danger is if you roll something that DOES make sense. Borkorud the Enraged, god of Flame and Battle with the symbol of the sword? Dude, that's BORING.
Whoops, almost forgot about alignment there. Tell you what; make him whatever alignment you want, preferably fairly close to the cleric worshiping him. Any seeming incongruities will just add more texture. Got an evil Sun god? He's the god to the drought, the Sun burning crops and drying up wells. Got a good Murder god? She's the god of retribution, killing those whom justice and vengeance demands.
See you all in church!