Ysmir is the Nordic aspect of Talos. According to the Greybeards, the name 'Ysmir' is, in fact, 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.
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 sorrow await Stormcrown, with no worthy head rest on. By our Dragon shout, Dragonborn, we give it now, by power of Kyne, by power of Shor, by power of Atmora of the old. Come now Ysmir, Dragon of the North. Remember this he.".