Note: Most cheats can only be entered once per campaign, and some will not work after another cheat is entered.
Press the tilde (~) key (or the key above Tab) to bring down the console, and input one of the following:

bestbuy: Units are 10% cheaper.
jericho: Walls will crumble.
add_money 20000: Adds money. X = amount.
add_population Y X: Adds population, where Y is the settlement name and X the amount.
auto_win attacker/defender: Attacker or defender automatically wins the next auto resolved battle.
create_unit settlement/charactername unit_ID amount exp/armor/weapon: Creates a unit in the selected settlement or characters army with the stats you input
toggle_fow: Toggles Fog of War
give_trait characternname traitname level: Gives the character the trait at the chosen level.
list_traits: Lists all traits
move_character Z X,Y: Moves character to location, where Z is character name and X Y are coordinates.
force_diplomacy accept/decline/off: Forces opponent to accept diplomatic proposal
invulnerable_general charactername: General is invulnerable in combat
season summer/winter: changes season
process_cq "name of settlement": All building in settlement is completed, this only works on one settlement at a time.
disable_ai: Raom the map freely without attacks

Enter process_cq settlement and all buildings in a settlement are done. Can only use once per game.


Patch 3.1 disables the one use per game limit.
 

Bring up the cheat console by pressing the key above Tab (usually "~"). Enter the codes below for the desired characters:

give_ancillary "character name" "catamite" - Gives spy / assassin this +1 subterfuge
give_ancillary "character name" "courtesan" - Gives Spy / assassin +1 subterfuge
give_trait "character name" "GoodDiplomat" 1-5 - Gives any character between 1-5 influence
give_trait "character name" "GoodSpy" 1-5 - Gives any character between 1-5 subterfuge
give_trait "character name" "GoodAssassin" 1-5 - Gives any character between 1-5 subterfuge

Enter oliphaunt in the drop console. This creates elephants that are 40% bigger in campaign mode and may interfere with other cheats.

Beat the game once to unlock Egypt, Gaul, Germany and Spain as starting nations.