Daeron I Targaryen, The Young Dragon, was the eldest son of Aegon III and the eighth Targaryen king to sit the Iron Throne from 157-161 AC. He ascended to the throne at the age of fourteen and is famous for conquering Dorne, which he wrote about in his Conquest of Dorne.
King Aenys I Targaryen by Amok. "A weakling. As tall as his father Aegon, but softer looking. Slender, weedy, dreamy.... His smile should be somehow tenuous, nervous, anxious to please." - GRRM's description to the artist.