Ultimate Summoner (3.5e Optimized Character Build)
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This is the person who makes all the monsters they summon so much more powerful than they normally are.
3.5e PHB, 3.5e DMG
 Game Rule Components
 Spells, Powers, Soulmelds, Stances, etc...
None really needed
Starting Ability Scores (Before Racial Adjustments): You'll want a high Intelligence and high Wisdom (at least 17) for this one.
Alignment Any nongood
|Saving Throws||Feats|| Class
|1st||Wizard 1||+0||+0||+0||+2||Extend Spell, Tattoo Focus||Summon Familiar, Scribe Scroll||Max out Spellcraft, Know(Arcana), and Know(Religion). Specialize in Conjuration (Do NOT prohibit Transmutation)|
|2nd||Wizard 1, Cleric 1||+0||+2||+0||+4||Turn/Rebuke Undead||Continue to max out Spellcraft, Know(Arcana), and Know(Religion). (Plant or Elemental domains suggested)|
|3rd||Wizard 2, Cleric 1||+1||+2||+0||+5||Maximize Spell||Continue maxing out Spellcraft, Know(Arcana), and Know(Religion).|
|4th||Wizard 2, Cleric 2||+2||+3||+0||+6||Continue maxing out Spellcraft. Ability Score increase +1 Int|
|5th||Wizard 3, Cleric 2||+2||+4||+1||+6||Continue maxing out Spellcraft.|
|6th||Wizard 3, Cleric 3||+3||+4||+2||+6||Empower Spell|
|7th||Wizard 3, Cleric 3, Mystic Theurge 1||+3||+4||+2||+8||+1 Arcane casting/+1 Divine casting|
|8th||Wizard 3, Cleric 3, Mystic Theurge 2||+4||+4||+2||+9||+1 Arcane casting/+1 Divine casting||Ability Score increase +1 Int|
|9th||Wizard 3, Cleric 3, Mystic Theurge 2, Red Wizard 1||+4||+4||+2||+11||Spell Focus (Conjuration)||Enhanced Specialization, Specialist Defense +1, +1 Arcane casting||Do NOT prohibit Transmutation|
|10th||Wizard 3, Cleric 3, Mystic Theurge 2, Red Wizard 2||+5||+4||+2||+12||Spell Power +1, +1 Arcane casting|
|11th||Wizard 3, Cleric 3, Mystic Theurge 3, Red Wizard 2||+5||+5||+3||+12||+1 Arcane casting/ +1 Divine Casting|
|12th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 2||+5||+5||+3||+13||Greater Spell Focus (Conjuration)||+1 Arcane casting/ +1 Divine Casting||Ability Score increase +1 Int|
|13th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 2, Thaumaturgist 1||+5||+5||+3||+15||Improved Ally, +1 Any Casting||Increase your Wizard Casting|
|14th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 2, Thaumaturgist 2||+6||+5||+3||+16||Augment Summoning, +1 Any Casting||Increase your Wizard Casting|
|15th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 2, Thaumaturgist 3||+6||+6||+4||+16||Feat||Extended Summoning, +1 Any Casting||Increase your Wizard Casting|
|16th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 3, Thaumaturgist 3||+6||+7||+5||+16||Specialist Defense +2, +1 Arcane Casting||Ability Score increase +1 Int|
|17th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 4, Thaumaturgist 3||+7||+7||+5||+17||Spell Power +2, +1 Arcane Casting|
|18th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 5, Thaumaturgist 3||+7||+7||+5||+17||Feat||Bonus Feat, Circle Leader, +1 Arcane Casting||For the Bonus Feat choose Spell Mastery, and master your best Summoning and Enhancement Spells|
|19th||Wizard 3, Cleric 3, Mystic Theurge 4, Red Wizard 6, Thaumaturgist 3||+8||+8||+6||+18||Spell Power +3, +1 Arcane Casting|
 Other Components
Basically what this does is it lets you conjure as a Lv 19 Wizard (though your other spells are cast as a Lv 16), and your summons get +4 Strength and Constitution as well as staying summoned twice as long as normal (four times if you Extend the spell).
 Munchkin-Size Me
Spell-Storing Weapons and Rings are always excellent for the extra Summon.
Metamagic Rods help, especially Extend, which would get up to three of your Summons to last up to eight times as long.
 Side Notes
The reason why you don't want to prohibit Transmutation is because you can use many of those spells to enhance your summoned monsters, also healing it with your cleric spells isn't a bad idea
By choosing a Plant or Elemental domains, it allows you to control and/or turn monsters, which may be useful
With the Spell Mastery, you can summon monsters even when you've lost your spellbook.
Unless the DM says otherwise, your character has to have been born in Thay.
Your Reflex Save isn't great
 DM Counters
Antimagic would make them almost helpless, as well as silence spells (unless they take the Silent Spell feat), also, enemies that are adept at banishing would give the Summoner a hard time.