This is the official summoner history written by Square Enix. It was sold in Japanese books long ago. Enioy.
The italic comments are not in the book, but are personal comments.

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Summoners are conjurers that make pacts with the gods themselves, calling them forth as avatars using forbidden magic.

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Evoker's Spats
Tights hug the upper thigh, while bands of leather attach the spats to the body below the knee. A small amount of astral essence is incorporated into the garment itself.

Evoker's Bracers
These gloves cover the arms up to the elbows. They are crafted from cloth and the structure is reinforced with leather.

Evoker's Pigaches
The toes in these leather shoes taper to a point, which make them a little difficult to walk in and cause the wearer to sway a little while walking. The Summoner's affinity with the avatars they summon causes this behavior to be transferred to them as well.

Evoker's Doublet
This loose fitting long-sleeved garment is made from cloth. The wide cuffs are embroidered making the whole doublet quite an ornamental piece of clothing.

Evoker's Horn
A headband with a horn set in the center. The angled horn originated as a way for a Summoner to more easily communicate with their avatar through telepathy. Karaha-Baruha researched and designed the original model.

The Vanishing “Doll Master”
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Some years ago, the Head of the Manustery, Uran-Mafran, suddenly vanished. Ildy-Goldy, a researcher of tuning forks in the Rhinostery, one day saw his visage inside a giant protocrystal. Anyone who gets close to Uran-Mafran and the protocrystals has their memories erased, but those who shared his class in magic school still remember him.

Ildy-Goldy and Uran-Mafran share a common past, having been trapped in the Dungeon of Darkness. The dungeon robs one of their power, but the Doll Master Uran-Mafran not only retained his magic, but came out stronger.

Now you must travel to the protocrystals of every region and discover what Uran-Mafran is plotting. Carbuncle needs your help!

Karaha-Baruha
http://i703.photobucket.com/albums/ww33/SenseiShotokan/SMNkarahabaruha.jpg

Twenty years ago, during the Great War, the was a hero named Karaha-Baruha, who saved the people of Windurst. In addition, he was Vana'diel's most powerful Summoner, known far and wide for his abilities. In recent years, the ban on Summoning magic has been lifted, and the Rhinostery has spearheaded a research program into understanding its properties.

However, it's rumored that the conjuring performed by the adventurers of today is much different than the magic of Karaha-Baruha. What's different about it? With the original great Summoner deceased, we may never know.

Abilities

Astral Flow
This secret technique allows a Summoner to draw out and avatar's full power. It requires the use of your entire magical essence to boost the avatar, who then can release that energy to make a devastating magical attack against the enemy.

Blood Pact
A Blood Pact is a unique order given to a summoned avatar that they must carry out. All avatars have a variety of different abilities they can utilize, and their repertoire increases along with the skill of their master.

Carbuncle
Carbuncle is the avatar of Light, who can be conjured forth magically. Carbuncle represents the bonds between humans and avatars and will come to the aid of all who choose to walk the path of a Summoner.

Fire Spirit
A Fire Spirit can be called forth after invoking the power of a written pact. Spirits are different from avatars, in that you cannot relay orders to them.

Weapons and Armor

Astral Signa
This magical staff topped with an ominous insignia once belonged to a magical country destroyed by the Orcs. The bottom was used to draw symbols as part of incantations to open gates to the astral plane. Upon receiving the staff, it became the Orcish general's secret treasure, until he gave it over to the Yagudo as a peace offering.

Archalaus's Pole
Long ago, there was an infamous Gigas sorcerer, named Archalaus. This short staff was his prized possession. Not only does the staff grant the wielder his cunning wisdom, but when they strike an enemy on the head, the staff has the haunting ability to steal their memories.

Carbuncle Mitts
Astral essence imbued within the interior cloth of these soft mittens gives the feeling of gently embracing Carbuncle. The cloth is from treasured garments known as Glittering Clothes passed down from Tonberry ancestors.

Errant Hat
If one wishes to become a great magic-user, it is recommended they take a pilgrimage to the various nations of the world, learning and experiencing everything they have to offer. This hat helps one to travel freely and not be caught up in the mundane conflicts of mankind by inviting in positive feelings and calm thoughts.

Austere Robe
Patched together with animal hides and cloth, this robe gives one a shabby-looking appearance. However, its true worth is not in the impression it makes on others. For some reason, avatars from the astral plane favor this look and it causes their bonds with a Summoner to strengthen.

Pictures and translated information are from Final Fantasy XI Life in Vana’diel, published by Enterbrain
http://www.jpbutton.com/ administrator for the in-depth translation.

Original post on Killing Ifrit Forums by SenseiShotokan.
http://killingifrit.com/forums/topic/175500-summoner-your-history/