Louis XXIV
Le Roi Soleil
I apologize if this is duplicative of the other thread suggesting leaders, but that's not my intent. The idea here is I'll list every Civ that's ever appeared in game. Some probably have the most obvious choice, but many others do not. While I suspect it's too late to change the ones that have been included, maybe it'll inspire Firaxis to shake things up for expansion packs. I would also suggest, rather than give 20-30 different suggestions, make a few suggestions and then defend why they're a good choice. I deliberately only included Civs already included in games so this doesn't become a "suggest a Civ" type thread.
I'll edit this post for as long as I'm able to include any leaders suggested. Let me know if I left any Civs out, I did this from memory:
Rome - Gaius Marius, Septimius Severus, Trajan, Scipio Africanus, Hadrian, Diocletian, Cicero, Sulla, Marcus Aurelius, Claudius
Greece - Leonidas, Themistocles, Cleisthenes, Lysander, Attalus I Soter, Agamemnon
Celts - Vercingetorix
Carthage - Hamilcar Barca, Mago I
England - Alfred, Edward I, Oliver Cromwell
France - Francis I, Louis IX, Henri IV, Philippe II Auguste, William the Conqueror, Napoleon III, Charlemagne
Germany - Otto I, Wilhelm
Russia - Ivan IV (Ivan the Terrible), Alexander II, Nicholas II
Spain - Charles I, Felipe II, Charles III
Portugal - Afonso Henriques
Dutch - William III, Wilhelmina, Philip the Good
Austria - Metternich, Franz Joseph
Sweden - Gustavus Vasa (Gustav I)
America - Theodore Roosevelt, Calvin Coolidge
Brazil - Getúlio Vargas
Poland - Jan III Sobieski, Sigmund August (Jagiellons)
Venice - Domenico Selvo
Holy Roman Empire - Otto I
Byzantines - Basil II, Alexios Komnenos, Manuel Komnenos, Nikephoros Phokas, Leo III the Isaurian
Denmark - Margarethe (Margaret I), Cnut the Great
Vikings - Harald Hardrada
Scandinavians
Persia - Nader Shah, Abbas the Great, Khosrau, Shapur II the Great
Babylon
Sumeria - Ur-Nammu, Shulgi
Egypt - Thutmose III, Akhenaten
Assyria - Semiramis (Shammuramat), Tiglath Pileser III, Sennacherib
Ottomans - Roxolana
Arabs - Baibars
China - Zhu Di (The Yongle Emperor), Taizong, Yang Jian, Cao Cao (Wei Wu Di), Kangxi (Qing Sheng Zu)
Japan - Meiji, Shomu
Mongolia - Ögedai
Korea - Myeongseong, Seondeok
India - Shah Jahan, Chandragupta II, Lakshmibai, Samudragupta
Indonesia - Tribhuwana
Polynesia - Kalakaua
Khmer
Siam - Naresuan
Mali
Songhai - Sunni Ali
Zulu - Cetswhayo
Ethiopia - Menelik II, Ezana
Iroquois - Decanesora, Joseph Brant (Thayendanegea), Aliquippa, Dekanawida
Sioux - Crazy Horse
Shoshone
Aztecs - Atotoztli, Ahuizotl, Nezahualcoyotl, Cuauhtemoc
Maya - Yohl Ik'nal, Lady Six Sky
Inca - Tupac Yupanqui
Native Americans - Tecumseh, Geronimo
I'll edit this post for as long as I'm able to include any leaders suggested. Let me know if I left any Civs out, I did this from memory:
Rome - Gaius Marius, Septimius Severus, Trajan, Scipio Africanus, Hadrian, Diocletian, Cicero, Sulla, Marcus Aurelius, Claudius
Greece - Leonidas, Themistocles, Cleisthenes, Lysander, Attalus I Soter, Agamemnon
Celts - Vercingetorix
Carthage - Hamilcar Barca, Mago I
England - Alfred, Edward I, Oliver Cromwell
France - Francis I, Louis IX, Henri IV, Philippe II Auguste, William the Conqueror, Napoleon III, Charlemagne
Germany - Otto I, Wilhelm
Russia - Ivan IV (Ivan the Terrible), Alexander II, Nicholas II
Spain - Charles I, Felipe II, Charles III
Portugal - Afonso Henriques
Dutch - William III, Wilhelmina, Philip the Good
Austria - Metternich, Franz Joseph
Sweden - Gustavus Vasa (Gustav I)
America - Theodore Roosevelt, Calvin Coolidge
Brazil - Getúlio Vargas
Poland - Jan III Sobieski, Sigmund August (Jagiellons)
Venice - Domenico Selvo
Holy Roman Empire - Otto I
Byzantines - Basil II, Alexios Komnenos, Manuel Komnenos, Nikephoros Phokas, Leo III the Isaurian
Denmark - Margarethe (Margaret I), Cnut the Great
Vikings - Harald Hardrada
Scandinavians
Persia - Nader Shah, Abbas the Great, Khosrau, Shapur II the Great
Babylon
Sumeria - Ur-Nammu, Shulgi
Egypt - Thutmose III, Akhenaten
Assyria - Semiramis (Shammuramat), Tiglath Pileser III, Sennacherib
Ottomans - Roxolana
Arabs - Baibars
China - Zhu Di (The Yongle Emperor), Taizong, Yang Jian, Cao Cao (Wei Wu Di), Kangxi (Qing Sheng Zu)
Japan - Meiji, Shomu
Mongolia - Ögedai
Korea - Myeongseong, Seondeok
India - Shah Jahan, Chandragupta II, Lakshmibai, Samudragupta
Indonesia - Tribhuwana
Polynesia - Kalakaua
Khmer
Siam - Naresuan
Mali
Songhai - Sunni Ali
Zulu - Cetswhayo
Ethiopia - Menelik II, Ezana
Iroquois - Decanesora, Joseph Brant (Thayendanegea), Aliquippa, Dekanawida
Sioux - Crazy Horse
Shoshone
Aztecs - Atotoztli, Ahuizotl, Nezahualcoyotl, Cuauhtemoc
Maya - Yohl Ik'nal, Lady Six Sky
Inca - Tupac Yupanqui
Native Americans - Tecumseh, Geronimo