The thu'um, also referred to as the Masculine Breath, the Storm Voice or simply the Voice, is a form of magic inherent in most Nords and some others which uses the words of the language of the Dragons to form "Shouts", the equivalent of spells, of immense power. The word actually means "shout" in the Dragon language. It is said that dragons make no distinction between debating and fighting, and so their words have always been magical and powerful, for those who take the time to learn and understand their meaning. The Nords believe that Kyne, the embodiment of the wind who is viewed as the Nordic aspect of Kynareth, breathed onto the land at the Throat of the World to form them. As such, the Nords believe that their voice and breath is their very essence, and that channeling this life essence is how the thu'um operates. Those who can wield this power are called Tongues by the Nords. Most, if not all, Nords have some capacity for the thu'um, but it takes particular talent and many, many years of study and training to become a Tongue. The thu'um can be used for a wide variety of purposes, anything from sharpening blades to quickly traveling across the land, even controlling animals or killing enemies. Some stories suggest that the ancient Tongues even had the power to "sing Shor's ghost into the world". The most powerful Tongues must be careful when they speak and are often gagged for safety, as their voice can cause great destruction.
Thu'um can be traced to ancient Atmora[UOL 1] with the first known human users of the Thu'um being the priests of the Dragon Cult, who were likely granted this ability from the bond they had with their respective Dragon lord.
In the late Merethic Era, the dragon Paarthurnax taught the Thu'um to the humans who would rebel against the Dragon Cult and their dragon overlords, who were worshiped as gods. These early Nords would become known as the Tongues, and began using their new-found Shouting abilities to slay the dragons. The three chiefs of the Tongues devised the shout Dragonrend to render Alduin temporarily mortal, but were unable to kill him and were forced to employ the use of an Elder Scroll to banish him. Most contemporary Nords believe the Thu'um was taught directly to mortals by the daughters of Kyne, while the truth and existence of Paarthurnax are kept secret.
Before and during the Skyrim Conquests around 1E 240, the greatest Nordic war chiefs were also Tongues: (Derek the Tall, Jorg Helmbolg, Hoag Merkiller). They needed no conventional siege weapons when attacking a city, instead using the Voice to shout down the gates and allow their armies to storm in. During the first Akaviri invasion in 1E 2703 the invaders faced Reman I in a climactic battle at Pale Pass. When they heard Reman's voice, they realized he was who they were searching for, and swore fealty to him.
In the early First Era, Skyrim's military suffered an ignominious defeat against Morrowind at Red Mountain. Present at the battle was Jurgen Windcaller, an extremely powerful Tongue. He was disturbed by the inability of the thu'um to secure victory, and meditated for seven years on "how Strong Voices could fail". His eventual conclusions formed the basis of the philosophy of the Way of the Voice, stating that the thu'um should only be used in times of true need, not as a routine tool of conquest. Since then, the most powerful Tongues have typically become Greybeards, a group of monks who live at High Hrothgar, a settlement near the summit of the Throat of the World, where they silently study, meditate, and train until if and when a time of true need arrives. They speak only on the rarest of occasions, such as to announce the destiny of the great Tiber Septim, who united Tamriel into the Third Empire and later became Talos, the Ninth Divine. In 4E 201, the Greybeards spoke again to call the Dovahkiin to High Hrothgar for instruction on how to use the thu'um.
A Dragonborn (or Dovahkiin in the Dragon tongue) possesses the ability not only to absorb the souls of slain dragons, but to thereby absorb knowledge of their language, thus learning in a short time what it would take other Tongues a lifetime of intense training and study to achieve.
Tongues are individuals who have the ability to use the Thu'um. They usually require a great deal of study and training to develop their power, but in some cases the power comes naturally to them.
Dragonborn, particularly those anointed by Akatosh, have extreme aptitude to learn and utilize Thu'um.
Ancient Nord Heroes
The Ancient Nord Heroes, described as the "the first mortal masters of the voice", were among the first Nords who learned the power of the Thu'um and were instrumental in Alduin's defeat during the Dragon War.
Great Nord War Chiefs
In the days of the conquest of Morrowind and the founding of the First Empire, several notable Nordic war chiefs were known to wield the Voice. Dunmer historical accounts vilify them as "demon chieftains" and remember some of them by other names.
- Hoag Merkiller
- Derek the Tall
- Jorg Helmbolg
- "Barfok, Maid of Planes"
- "Bhag, the Two-Tongued"
- "Chemua, the Running Hunger"
The Greybeards are an ancient and honored order of monks who preach a lifestyle of meditative study of the Thu'um, known as the Way of the Voice.
- Jurgen Windcaller
- Grundwulf (former)
- Ulfric Stormcloak (former)
- Olaf One-Eye
- Kvenel the Tongue
- Jorunn the Skald-King
- Ebony Warrior
- Zaan the Scalecaller
- Ysgramor [nb 1]
- Vahlok the Jailor [nb 2]
- Nurarion the Perfect [nb 3]
- Oskar the Fool 
Divine beings associated with the Thu'um and its usage
- ^ Despite predating the "first mortal masters of the voice" Ysgramor is described in Nordic legends with feats such as "Shouting Some Sense" into the Nords, and with "breath weighted with power sounds".[UOL 2] This could be due to a nature possibly interlinked with Dragons - be it that he was a literal Dragon,[UOL 3] or (more likely given his stature during the time period) he was a Dragon Priest.[UOL 4]
- ^ Vahlok is described in mythical accounts as using the Thu'um in his battle against Miraak. However its unclear how this was possible given the Ancient Nord Heroes (who came after him) were said to be the "first mortal masters of the voice".
- ^ Nurarion of Summerset was said to possess a voice that could "cut lightning bolts in half and turn mountains to rubble". This power was granted to him by Clavicus Vile in the Merethic Era. While its never explicitly called the Thu'um, these abilities align with its power. However it should also be noted (as with Vahlok the Jailor) he obtained this power before Paarthurnax first taught the Ancient Nord Heroes in the First Era.
- Akaviri swordsmen have been described as possessing a power similar to the thu'um, called "kiai".
- The Red Dome Templars (also known as the Red Templars) were unstable crusaders who drank the blood of Talos in order to obtain short-term martial shouting powers. They were hated by the rest of the Legion and a significant number of the members of the Elder Council wanted them dispersed. Due to this, they were mainly sent off to remote places like Morrowind.[UOL 5][UOL 3]
- Children of the Sky — A description of the Nords and the Thu'um
- ^ PGE
- ^ a b Varieties of Faith... — Brother Mikhael Karkuxor of the Imperial College
- ^ a b Paarthurnax's dialogue in Skyrim.
- ^ a b c d e Pocket Guide to the Empire, 1st Edition: Skyrim — Imperial Geographical Society, 2E 864
- ^ Five Songs of King Wulfharth
- ^ The Guardian and the Traitor — Lucius Gallus
- ^ Zaan the Scalecaller's dialogue in ESO: Dragonbones
- ^ The History of Zaan the Scalecaller — Jorvuld Davaux, Dragon Priest Historian
- ^ The Dragon War — Torhal Bjorik
- ^ Events of Alduin's Bane in Skyrim
- ^ a b Children of the Sky
- ^ The Rise and Fall of the Blades — Anonymous
- ^ The Etched Tablets of High Hrothgar.
- ^ Events of Dragon Rising in Skyrim
- ^ a b Events of The Way of the Voice in Skyrim
- ^ Five Songs of King Wulfharth
- ^ Throw Voice word wall in Skyrim
Note: The following references are considered to be unofficial sources. They are included to round off this article and may not be authoritative or conclusive.