A Dragonborn, (transliterated from to Dovahkiin in the Dragon language), is a rare individual who has been born with the blood and soul of a Dragon, but the body of a mortal, and can naturally learn and speak their ancient and powerful tongue, called the Thu'um.
Dragonborn scarcely exist, and it is rare for more than one to appear within an era. They can belong to any race or gender, since the Dragon blood (transliterated from to Dovah Sos) is a "gift" bestowed to certain mortals favored by Akatosh.
Some Dragonborn individuals have knowledge of the Thu'um, and can consume a slain Dragon's soul and absorb its knowledge, allowing them to learn Words of Power quickly. It is said that the Blades have always guided, protected, and served the Dragonborn, whom they consider "The ultimate Dragon slayer".
The Prophecy of the Dragonborn, generally attributed to the Elder Scrolls, and sometimes to the ancient Akaviri, tells that, at the end of time, in the wake of the World-Eater, the wheel will turn upon the "Last Dragonborn".
Dragonborns in History
The first Dragonborn in history was Miraak, a Dragon Priest from the Merethic Era. Instead of using his Dragonborn powers to fight Alduin, Miraak decided to serve Hermaeus Mora instead, making himself an enemy of the Dragon Cult he once served. He was eventually defeated by the Dragons and hid in Apocrypha, failing to complete his destiny to destroy Alduin. He was later encountered and ironically destroyed in the Fourth Era by the Last Dragonborn. 
The next Dragonborn was purportedly Saint Alessia, the Nedic slave queen who was blessed by Akatosh and given the Amulet of Kings to seal the covenant between them. This began the tradition of all legitimate rulers of the Cyrodilic Empire referred to as Dragonborn, as only they could wear the Amulet of Kings and light the Dragonfires in the Temple of the One.
Tiber Septim, founder of the Septim Dynasty of Tamriel, was the next individual to be recognized as Dragonborn. His heirs continued the tradition and were all considered Dragonborn Emperors. This lineage ended with the death of Martin Septim during the Oblivion Crisis.
- Miraak - Former Dragon Priest dating back to the Merethic Era and purportedly the first Dragonborn individual.
- Alessia - Slave queen of Cyrodiil in the First Era who made a covenant with Akatosh.
- Reman Cyrodiil - Famed ruler of Cyrodiil who thwarted the Akaviri Invasion during the First Era.
- Wulfharth - Ancient warrior-king of Skyrim known for reinstating the traditional Nordic pantheon.
- Tiber Septim - Legendary ruler who united Tamriel under his banner in the Second Era.
- Septim Bloodline - The lineage of Tiber Septim's successors. These include Martin Septim and Uriel Septim VII.
- Last Dragonborn - Legendary hero of prophecy who appeared in Tamriel during the Fourth Era. Also known as the Dovahkiin and the last recorded individual to be granted the dragon blood. Renowned for defeating Alduin, as well as Harkon and Miraak.
- Mankar Camoran - Altmer leader of the Mythic Dawn. In the first volume of his Commentaries, Mankar is said to be able to "speak with another tongue" and "speak fire". This, coupled with the fact that he could wear the Amulet of Kings in his Paradise, could imply that he was Dragonborn.
- To address the confusion that arose from the existence of a Dragonborn predating Alessia, Michael Kirkbride, former writer at Bethesda revealed "Alessia didn't have the power to absorb dragon souls. Hers was a much more nuanced power: to dream of liberty and give it a name and on her deathbed make Covenant with the Aka-Tusk." [OOG 1]
- The Nerevarine was referred to as "Dragon-born" in The Lost Prophecy, but the explanatory notes of this text claim this means they were part of the Empire.