The Dayne line went unbroken through the War of Five Kings, continuing through both the young Lord Edric Dayne, Squire to Beric Dondarrion and Lord Gerold Darkstar, of High Hermitage. Ulrich Dayne was the direct descendent of Edric Dayne.
Born to Arthur Dayne, Ulrich was the second-youngest of four sons. His older brothers were twins, and Cailin became a Maester while Jon abandoned his inheritance to seek adventure in Essos. After the birth of Martyn, his father later remarried and had two daughters, Ashara Dayne and Arianne Dayne.
Ulrich was raised by his father and brothers to become a great warrior and the Sword of the Morning. He was known throughout the realm as being an exceptional swordsman, and this was one of the reasons King Harys chose him for his Kingsguard.
Ulrich Dayne was a knight of King Harys' Kingsguard, who fought in the Battle of the Rainwood and became a paramour to Princess Sarella Martell. He sailed to Bloodstone after an an informant revealed the council held there and confronted Varyo Velaryon about the planned usurption. After killing Varyo's father figure and several of his men while under Guest Right, Ulrich was taken prisoner and his ancestral sword Dawn was confiscated. Ulrich was presumed dead by the realm, but later resurfaced in the Stormlands to lead a rebellion against the newly crowned King Damon Lannister.
Ulrich and his men were defeated at Stonehelm, and he and his brother Martyn Dayne were taken hostage back to King's Landing to negotiate a truce with Dorne. Queen Aeslyn Targaryen urged Ulrich to beg for a trial by combat, and then chose her dragon to be her champion. Ulrich slayed the dragon, but King Harys had already lost the war and so he was freed of his vows and allowed to return home.
After Sarella Martell wed Martyn Dayne, Ulrich confessed his love for the Princess to his brother, along with their affair. He then sabotaged Sarella's plans to assassinate King Damon, rescuing the Lannister and delivering him back to King's Landing in fullfillment of a promise made to the mad Queen. Afterwards, he left the capital for Essos in search of Dawn, which was rumored to have surfaced in Myr. He found the sword in the collection of a Magister, who offered to return it to Ulrich in exchange for his help in defeating Khal Joro. Atfer defeating the Khal and claiming the sword, Ulrich returned to King's Landing and swore himself to Damon, who named him Lord Commander of his Kingsguard.
Ulrich and Damon had a difficult relationship, and after some missteps he earned the distrust of the newly crowned Queen Danae Targaryen, as well. After revealing Thaddius Lannister's presence in the capital to Loren Lannister, Ulrich was given a trial by combat for breaking his oath to keep the King's secrets and called for a volunteer to fight him. Believing Ulrich to have fathered a child on Sarella, his brother Martyn accepted and killed him.
"The Sword of the Morning he may have been the first time you bedded him, but Ulrich Dayne died a one armed, useless drunk. A cripple. An oathbreaker. An idiot. I’ve never met anyone with his head so far up his own ass as your knight. His greatest feat was managing to both simultaneously worship and pity himself in amounts so astounding it’s a wonder he found time for anything else, like his duties, or more often than not, his wineskin." - Danae Targaryen to Sarella Martell
"Knights are the most honorable of all men, according to her story books, and the Sword of the Morning is the most honorable of all knights." - Sarella Martell
"The Great Dragonslayer, Ser Ulrich Dayne, the finest sword in all of Westeros, champion of tourneys, wielder of Dawn, former Knight of the Kingsguard who remained loyal to his vows and his honor... Oh, your celebrity must be such an awful burden to bear. I imagine you cry yourself to sleep at night, dabbing at the tears in your violet eyes with the silken small clothing of the noble ladies who flock to your bed." - Damon Lannister
"Even now Aemon's breath caught at the sight of the Sword of the Morning, a member of the King's own Kingsguard, wielding the greatsword Dawn like a milky white beacon." - Blood and Whispers (Chapter 1)
"I watched as my father - my real father, not my blood one - died in my arms, unable to choke out any last words, murdered by a man who I had minutes earlier given guest rights, a man who I had eaten with, who they called the most honorable man in Westeros. As I watched the life drain from the eyes of the man who raised me, I knew this; I didn't want to hurt anyone in my life, more than I wanted to hurt Ulrich Dayne. Damon did him a kindness." - Varyo Velaryon
"You truly don't see yourself as the hero people know you to be? You are a knight of the Kingsguard. You are the protector of the realm. You are the defender of the defenseless. The shield of the righteous. You wield a blade forged from the heart of a falling star. You are the Sword of the Morning." - Sarella Martell
"You fucked a loose woman and were surprised when she betrayed you; you followed an idiot king who did nothing but feast and frustrate his bannermen; you stupidly confessed the treachery of your brother's wife to him on his wedding day; you lost your sword through your own fault, and made a pact with a mad dragon queen and were burned. Oh, Ulrich, sorrow is not what you should be feeling, it is shame. Each of the events that have led you to these pitiful circumstances can be attributed to your own foolishness, and nothing else." - Damon Lannister
"Some would say you are the Sword of the Morning. Some call you Lord Commander. Others call you Dragonslayer. To Martyn Dayne you would be the brother who fucked his wife, and to the Princess Sarella you are a paramour. My husband thinks you are a man who forgets his position, and I think you are a fool if your pride and arrogance keep you from choosing to live." - Danae Targaryen
Arthur Dayne, father (deceased)
Jon Dayne, brother
Cailin Dayne, brother
Martyn Dayne, brother
Ashara Dayne, sister
Arianne Dayne, sister