Aemon Targaryen (Dragonknight)

Aemon Targaryen is an unseen character in Game of Thrones. He is long dead by the time of the series. He was a Prince of the Targaryen dynasty and the namesake of Maester Aemon. He was the uncle of Maester Aemon's grandfather, King Daeron II.

Background
Prince Aemon was called "the Dragonknight" on account of his heritage. He was raised to the Kingsguard at age 17 and eventually became Lord Commander. According to tradition, he was once saved from a snake pit by his cousin Baelor I Targaryen, whom the snakes refused to bite. He fought and barely defeated Lord Cregan Stark. He also wielded Dark Sister, the Valyrian steel sword of Visenya Targaryen.

Season 4
Aemon the Dragonknight's deeds are recorded in The Book of Brothers.

In the books
In the A Song of Ice and Fire novels, Aemon was knighted young and joined the Kingsguard at the age of seventeen. He served under four kings: His cousins Daeron the Young Dragon and Baelor the Blessed, his father Viserys II, and his brother Aegon the Unworthy. Aemon has been referred to as the noblest and greatest knight that ever lived and his skills with a sword were legendary throughout Westeros.

Aemon took part in the conquest of Dorne, led by his cousin and king, Daeron I. Aemon won great fame by defeating a Dornish champion, and was present several years later after a rebellion in Dorne undid Daeron's conquest, and in which Daeron himself was killed. Aemon was taken captive by the Dornish, and put in a cage, placed above a pit filled with vipers. He was eventually saved by his cousin and new king, Baelor I.

Songs speak of his doomed love for his brother's queen, his own sister, Naerys. He supposedly cried when Naerys married their brother. After his brother Aegon became king, rumors started to spread that Aemon was the actual father of Aegon's son and heir, Prince Daeron. He defended his sister when she was accused of treason by the knight Ser Morgil.

Aemon once fought Cregan Stark. Prince Aemon claimed he had never faced a finer swordsman.

Aemon once won a tourney, disguised as a mystery knight, after his brother had forbidden him from participating because he wanted to name his mistress at the time the Queen of Love and Beauty. Aemon took part secretly under the disguise of The Knight of Tears, and was thus able to crown his sister Naerys the Queen of Love and Beauty, in place of the king's mistress.

Despite the difficult relationship between Aemon and his brother, Aemon died honorably defending his brother and king from the brothers of Ser Terrence Toyne, who wanted to assassinate Aegon IV in revenge for him executing Terrence for sleeping with his mistress.

Maester Aemon explicitly states that his grandfather Daeron II named him after Aemon the Dragonknight, who was Daeron II's uncle - though Maester Aemon notes there are those who said that the Dragonknight was actually Daeron II's own father, depending on which tale you believe.