Thu'um

The Thu'um, also referred to as Storm Voice or simply the Voice, is a form of magic that most Nords and some others possess which utilizes the Dragon Language to form Dragon Shouts, of immense power. The word itself directly translates to the word "shout" in the Dragon language. Most shouts are made up of three words of power.

Beginning
In the early ages of Nirn the only beings capable of using the Thu'um were the dragons, the children of Akatosh. The Thu'um was part of their natural language and could be utilized as a weapon. They abused this power to bring havoc upon the races of man during the late merethic era. Among the leader of the dragons was Alduin, the World-Eater, who took to his belief that he was a deity and claimed his father Akatosh's place. Humans who worshiped the dragons were part of the Dragon Cult.

Human rebellion
Kyne had pitied man and tasked Paarthurnax, Alduin's younger brother and second-in-command, to betray the Dragons and teach man the way of the voice. The humans then used the voice to fight the dragons, and had created their own shout, Dragonrend. They then used this shout, along with an Elder Scroll, to send Alduin through time and end the age of the dragons.

Miraak and Hermaeus Mora
Miraak, a Dragon Priest, discovered he was the first Dragonborn. He betrayed his order and sought knowledge from Hermaeus Mora, a Daedric Prince. Mora taught him the shout Bend Will, a unique shout which could force people and dragons to do his bidding. He used this shout to create an army, but in his foolishness believed he could take on all the dragons. The dragons fought him and tore Solstheim from Skyrim in a battle. Miraak was almost defeated but was saved by Hermaeus Mora. His temple was then destroyed and the dragons free from his rule. Miraak was also asked to help defeat Alduin, but refused.

Miraak's knowledge had grown so much that he managed to learn a shout with four words, abnormal for any dragon or man.

King Wulfharth
King Wulfharth was a Dragonborn and had mastery over the Thu'um. It is said his Thu'um was so powerful that he could not verbally swear into the office, and scribes were used to draw up his oaths. He learnt it when watching battles of using the Thu'um.

Creation of the Greybeards
In time man too had abused the voice. Instead of using it as a form of prayer or use of self-defense, they instead used it as a mere weapon. Jurgen Windcaller founded the Greybeards on the Throat of the World and taught man to instead use the Thu'um as a force of peace and enlightenment, a teaching which now remains in the Greybeard code. Many greybeards have such a powerful Thu'um they could cause major destruction with a simple sentence.

Tiber Septim
The future Emperor of the Septim Empire, Tiber Septim, also known as General Talos was a Dragonborn taught by Wulfharth how to use the voice. He made his way up the Throat of the World and entered High Hrothgar. The Greybeards told Talos that he would become the chosen one who would defeat the Elves and become Emperor of a united Tamriel.

Ulfric Stormcloak
Ulfric Stormcloak was the Jarl of Windhelm who was taught under the Greybeards on how to use the voice. He then grew up to abuse this power and use it in combat against High King Torygg and created the Stormcloak Rebellion.

However, Ulfric mentions to the Dragonborn that he still doesn’t take the Thu'um lightly even though he can’t completely tale to its philosophy.

Last Dragonborn and Alduin
A hero called the Last Dragonborn was a prisoner, about to be executed at Helgen in 4E 201. Before their execution could happen, Alduin, the World-Eater, showed up after his travel through time and destroyed the town. This granted the hero with an escape.

The Last Dragonborn then slayed Mirmulnir and discovered they could absorb Dragon souls. They then used the Thu'um and were called upon by the Greybeards, who shouted "Dovahkiin."

The Dragonborn was then journeyed up High Hrothgar and trained with the Greybeards. They then went on a mission to find out how to defeat Alduin and prevent the world's destruction.

After discovering how to defeat Alduin, the Dragonborn then went on to defeat Alduin using the Thu'um in Sovngarde.

Last Dragonborn and Miraak
At some point the Last Dragonborn was ambushed by a group of cultists sent by Miraak. Upon investigating and arriving on Solstheim, the Dragonborn then discovered who Miraak was and how his history tied in with theirs.

Upon completing multiple tasks for the Skaal and Hermaeus Mora, the Last Dragonborn then learned the Bend Will shout, freed the All-Maker stones and Solstheim from Miraak's grasp and traveled to Apocrypha to defeat Miraak. During this the Thu'um was used extensively, and was even known to have had a four word shout involved.

Learning
The Thu'um can be taught through many means to men, mer and beastfolk alike. Individuals who are Dragonborn can learn the Thu'um faster.

Training
While the Thu'um can easily be learnt by Dragonborn, it takes a much longer time to learn for regular people. Ulfric Stormcloak spent around ten years training with the Greybeards to learn the Thu'um.

Word Walls
Words of power can be learnt from Word Walls found throughout Tamriel. Each wall often contains one word, and can only be used by those with the knowledge of the Thu'um.

Passing of knowledge
Shouts and words of power can be passed on from one another. This is demonstrated by the greybeards.

Dragons

 * Alduin
 * Paarthurnax
 * Odahviing
 * Durnehviir

People

 * Miraak
 * Gormlaith Golden-Hilt
 * Hakon One-Eye
 * Felldir the Old
 * Wulfharth
 * Tiber Septim
 * Last Dragonborn
 * Ebony Warrior

Greybeards

 * Jurgen Windcaller
 * Arngeir
 * Borri
 * Wulfgar
 * Einarth