When you build a temple, you can purchase a deity for your civilization at the cost of 1000 piety. There are 4 different deities of which you can only choose one per reset.
If you do reset the game you may choose an additional deity after building the temple, and/or remove an old deity for another 1000 piety in return for gold (iconoclasm)
(The amount of the 3rd needed material increases on each purchase)
Deity of Battle
| Build Altar | 200 stone, 200 piety, 100 metal: +1 devotion | |
| 10d | Riddle of Steel* | 1000 piety: Improve soldiers |
| 20d | Smite Invaders | 100 piety per invader |
| 30d | Throne of Skulls* | 1000 piety: Slaying enemies creates temples |
| 40d | For Glory! |
1000 piety: Temporarily makes raids more difficult, increases rewards |
| 50d | Lament of the Defeated* | 5000 piety: Successful raids delay future invasions |
Deity of Cats
| Build Altar | 200 stone, 200 piety, 100 herbs: +1 devotion | |
| 10d | Lure of Civilisation* | 1000 piety: increase chance to get cats |
| 20d | Pest Control | 100 piety: Give temporary boost to food production |
| 30d | Warmth of the Companion* | 1000 piety: cats help heal the sick |
| 40d | Grace | 1000 piety: Increase Happiness |
| 50d | Comfort of the Hearthfires* | 5000 piety: traders marginally more frequent |
Deity of Fields
| Build Altar | 500 food, 500 wood, 200 stone, 200 piety: +1 devotion | |
| 10d | Blessing of Abundance* | 1000 piety: increase farmer food output |
| 20d | Burn Wicker Man | 500 wood, 1 worker: random bonus to a resource |
| 30d | Abide No Waste* | 1000 piety: workers will eat corpses if there is no food left |
| 40d | Walk Behind The Rows | 1 worker per second: boost food production (on/off) |
| 50d | Stay with us* | 5000 piety: traders stay longer |
- Deity of the Underworld
| Build Altar | 200 stone, 200 piety, 1 corpses: +1 devotion | |
| 10d | Book of the Dead* | 1000 piety: gain piety with deaths |
| 20d | Raise Dead | 100 piety per zombie |
| 30d | A Feast for Crows* | 1000 piety: corpses are less likely to cause illness |
| 40d | Summon Shades | 1000 piety: Souls of the defeated rise to fight for you |
| 50d | Secrets of the Tombs* | 5000 piety: graveyards increase cleric piety generation |
The Underworld deity is probably the most powerful and useful deity in the game, mostly because it makes food (and therefore mills) and housing completely irrelevant as soon as you're in the late game. With a few thousand clerics, you can start replacing your population with Undead by sending them up against factions that they stand no chance against. The best way to manage this is to remove one batch of humans from a proffession and add them to your army, then send them into battle. Note that you will gain the corpses of your enemies as well as the corpses of your allies. Make sure your graveyards are all full before you do this, or you'll end up wasting a lot of good corpses. Again, make sure you have a few thousand Clerics first (like, 10,000, at the least) or you'll end up with a lot of sick people regardless of whether you have A Feast For Crows or not.
To Zombify your clerics safely, make sure you start off with a force of human soldiers roughly equal to that of your clerics and getting them killed. Then swap your clerics into your soldier slot and put the Zombies in the cleric slot. I'd strongly recommend Zombifying your farmers last so that you can control what resources you're being deprived of; it's especially important to make sure mining isn't emptied before you're ready because metal and leather are vital to your soldiering.
Zombies function identically to normal humans and benefit from all upgrades, but do not need to eat and make no use of housing. You do not lose anything by Zombifying your workforce. Currently, my CivClicker account has 0 humans and 3 848 999 Zombies, and I haven't had to buy new workers in forever. Losing a battle is no longer a punishment--just resurrect your soldiers, along with the enemies you killed, and try again. I'd recommend making sure you have a fairly large number of Clerics to maintain your fighting force--but unlike normal, human soldiers, you won't need to continue increasing your Cleric population once you get to a point where you can zombify roughly 200,000 corpses at a go.
(Keep some farmers, though. You still need skins and leather.)
Credit: Snowskeeper
Pantheon Upgrades
Certain deity upgrades are added to your "Pantheon Upgrades" list, and are not lost if you reset your civilization. These upgrades are indicated above with an asterisk (*).
At the start of a new game (reset game), iconoclasm appears in the deity tab and costs per 1000 piety. This is considered the most useless upgrade in game as it eliminates all pantheon upgrades with a gold reward depending on devotion.
The deity of underworld is considered the easiest economically and for raiding as you can create zombies with corpses and 100 piety. These zombies have consistent prices, don't need food, houses and cannot get sick. One possible disadvantage is zombies will always have a happiness ranking of 'content' and may dilute the happiness, preventing blissfulness from being achieved