Ysmir is the Nordic aspect of Talos. According to the Greybeards, the name "Ysmir" is also a title which means "Dragon of the North." It was given to the Emperor Tiber Septim, who withstood the power of the Greybeards' Thu'um; they recognized him as a Dragonborn and gave him the title.
Ysmir the deity is the Nordic aspect of the Imperial God known as Talos, after he had been called to High Hrothgar by the Greybeards to conquer Tamriel. On his death, he became Talos in the Imperial Pantheon, and Ysmir in the Nordic one.
Ysmir Wulfharth was an Atmoran born Nordic King during the First Era. His Thu'um was said to have been greatly powerful. Originally, Wulfharth thought he was called by the Greybeards when they were calling for Talos. But when he arrived, he was destroyed by their voices, as he was not the one destined to unite Tamriel.
Tiber Septim was a Dragonborn who was granted the title by the Greybeards. He was also the first Emperor of the Third Era and the first member of the Septim dynasty, as well as the first Emperor to rule over the entirety of Tamriel after using the Numidium to defeat the Second Aldmeri Dominion. He is widely believed to have ascended to Godhood and having become Talos, though his worship has been legally banned in the empire by the White-Gold Concordat. The most common belief is that he was born in Atmora under the name of Talos, which means "Stormcrown", that he grew up in Skyrim and became General of the Colovian Estates under King (and later Emperor) Cuhlecain. That he met the combined army of Skyrim and High Rock, who were hostile to Cuhlecain, on the cliffs of Sancre Tor and that the former joined him when they saw him use the Thu'um and saw he was Dragonborn. Another less common belief is that he was born in Alcaire, High Rock, under the name of Hjalti Early Beard and that, instead of only using his own Thu'um against the reachmen, was aided by none other than Wulfharth (then known as the Ash-King, Ysmir the Grey Wind, Storm of Kyne), who he later betrayed in order to power the Mantella and be able to use the Numidium. Either way, in both versions he adopts the name of Tiber Septim and is arguably the most influential and known of the individuals who were granted the title of Ysmir by 4th Era 201.[source?]
The Last Dragonborn
During the events that unfold in The Elder Scrolls V: Skyrim, after completing "The Horn of Jurgen Windcaller," the Greybeards greet the Last Dragonborn in the dragon tongue with the words: "Lingrah krosis saraan Strundu'ul, voth nid balaan klov praan nau. Naal Thu'umu, mu ofan nii nu, Dovahkiin, naal suleyk do Kaan, naal suleyk do Shor, ahrk naal suleyk do Atmorasewuth. Meyz nu Ysmir, Dovahsebrom. Dahmaan daar rok.". This can be translated by: "Long has the Stormcrown languished, with no worthy brow to sit upon. By our breath, we bestow it now to you, in the name of Kyne, in the name of Shor, and in the name of Atmora of Old. You are Ysmir now, the Dragon of the North, hearken to it."