Civ VI leader trait ideas.

Philosophical-creative, mountain siege, Intellectual: +10% Beakers (science). 1/2 cost: library & laboratory. Desert warfare, Industrious, Military strength, Blessings of the Sea.

New traits: mountain siege-civilization produces mountain infantry units that start with Mountain artillery promotion (unit has small mountain cannon designed to disassembled and packed in mountainous terrain) that gives them collateral damage, ranged attack & siege abilities. Military strength-units within your own/ally border receive a +10% strength bonus. Blessings of of the Sea-Each fishing boat produces +2faith/culture.

New promotions: Mountain artillery-unit has small mountain cannon designed to disassembled and packed in mountainous terrain that gives them collateral damage, ranged attack & siege abilities. Indirect Fire.

New Unit: Mountain infantry-23 Str, Special abilities: mountain siege- mountain infantry units start with Mountain artillery promotion . Attack bonus of +3 in mountain terrain.
Promotions: Indirect Fire, mountain artillery, strength, Combat, Ambush I, desert combat I and all promotions open to infantry & siege units. Promotions started with- mountain artillery, strength, Combat IV, Ambush I & desert combat I.

Strategist - An AI that is actually smart. Uses strategy and out manoeuvres the player. Works best for Alexander and Genghis Khan.

Colonialist- for the British, Greeks and Carthaginians(Dutch, Portuguese, Spanish, Japanese, French and Vikings not excluding)

insanity - caligula (romans). random acts, chooses random techs and periodically will raze one of its own cities, or attack another civs city, at random. and makes irrational demands and threats regardless of ability to act on them. influences weaker minded rulers of civs to be vassals purely from fear and can use these to attack rival civs or each other or do the city razing.

it would be interesting trying to play caligula as a player; perhaps you would be actually given the role of his chief of staff trying to hold together the empire when he keeps randomly changing your tech choices and declaring war with no warning...probably impossible to implement in civ tho.

How about unique leader traits? (paired with unique civilization ability)
Basicly every leader would have two traits (like in CIV4) but now one from the leader and one from the nation.

Every leader should have their own, separate traits, the more different types of traits he/she was good at during his/her reign, the more they should be listed for them in the game.
Trait examples:
Pacifistic, Ruthless, Rational, Aggressive, Honorable, Highlander/Mountaineer(bonus food from mountain tiles), Seafaring, Colonial, Explorer, Defensive, Erratic, Scientific, Merchant, Charismatic, Commercial, Industrial, Wonder Builder, Agricultural, Artistic, Militarist, Spiritual, Opportunist, Politician, Tactician, Fanatical, some sort of Desert and/or Cold climate bonus trait, Aviator(some sort of plane bonus), and more.
All of these would come with some sort of bonus, each leader would have from 1 to 4 traits, depending on how good he/she was at each of these during his/her reign.