Theurge of Charisma (3.5e Optimized Character Build)
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Charisma based, instantaneous casters are my favorite, and this is my glorification of it.
Dungeon Masters Guide
 Race and Templates
Humans are always a good choice, but most any other race works with this. Races that add to Charisma are nice. Just stay away from races with penalty to charisma or that have level adjustment. (Catfolk may be an exception....)
Warmage, Favored Soul, Mystic Theurge.
Your feats will mainly depend on how you play the character, but dont overlook feats like Practiced Caster and Improved Initiative
 Spells, Powers, Items
Naturally, get a nice cloak of charisma!
 Ability Scores
Charisma is the most important because it is the primary casting ability for both classes. Wisdom helps with the DCs for favored soul DCs, and int helps with the damage done by warmage spells (warmage edge). Have a decent dexterity score, as the AC will be important. Hooray for elven chain!
Sample elite array: Str 8, Dex 14, Con 12, Int 10, Wis 13, Cha 15,
|1st||Favored Soul 1||Improved Initiative|
|2nd||Favored Soul 1/ Warmage 1||Armored mage (light), warmage edge|
|3rd||Favored Soul 2/ Warmage 1||Practiced Spellcaster (Favored Soul)|
|4th||Favored Soul 2/ Warmage 2|
|5th||Favored Soul 3/ Warmage 2||Deity's weapon focus|
|6th||Favored Soul 3/ Warmage 3||Practiced Spellcaster (Warmage)||Advanced learning|
|7th||Favored Soul 4/ Warmage 3|
|8th||Favored Soul 4/ Warmage 4|
|9th||Favored Soul 4/ Warmage 4/Mystic Theurge 1||Spell Penetration|
|10th||Favored Soul 4/ Warmage 4/Mystic Theurge 2|
|11th||Favored Soul 4/ Warmage 4/Mystic Theurge 3|
|12th||Favored Soul 4/ Warmage 4/Mystic Theurge 4||Greater Spell Penetration|
|13th||Favored Soul 4/ Warmage 4/Mystic Theurge 5|
|14th||Favored Soul 4/ Warmage 4/Mystic Theurge 6|
|15th||Favored Soul 4/ Warmage 4/Mystic Theurge 7||Spell Focus (Evocation)|
|16th||Favored Soul 4/ Warmage 4/Mystic Theurge 8|
|17th||Favored Soul 4/ Warmage 4/Mystic Theurge 9|
|18th||Favored Soul 4/ Warmage 4/Mystic Theurge 10||Greater Spell Focus (Evocation)|
|19th||Favored Soul 5/ Warmage 4/Mystic Theurge 10||Energy Resistance (1st type)|
|20th||Favored Soul 5/ Warmage 5/Mystic Theurge 10|
This is my realization of the armored caster. in this build, you can wear light armor without penalty (elven chain!!!) which gives you a decent AC (go give someone a shocking grasp, and survive the retaliation). You have a decent amount of spells, all which you can cast instantaneously. The focus of spellcasting onto one ability leaves some space to increase other abilities.