Aegon IV Targaryen

Aegon IV Targaryen, also called Aegon the Unworthy, is an unseen character in Game of Thrones. He is not expected to appear in the series, being long dead by the time it begins.

Aegon IV was the fourth king of his name to sit on the Iron Throne and the eleventh king of the Targaryen dynasty to rule the Seven Kingdoms. He was an ancestor of Viserys and Daenerys Targaryen. He was formally styled Aegon of House Targaryen, the Fourth of His Name, King of the Andals and the First Men, Lord of the Seven Kingdoms and Protector of the Realm.

Background
Aegon IV fathered several children, both trueborn and bastard. He was the father of Daeron II Targaryen and Daenerys Targaryen by his sister-wife, Queen Naerys Targaryen. With his cousin, Princess Daena Targaryen, he fathered Daemon and Serena Blackfyre.

Season 1
Aegon IV, along with his vast progenie, is mentioned in the House Targaryen's entry of the book The Lineage and Histories of the Great Houses of the Seven Kingdoms

In the books
In A Song of Ice and Fire, Aegon IV is remembered as one of the worst rules the history of Westeros, which is the reason why he's remembered as 'Aegon the Unworthy'. He was a decadent ruler who indulged his passions and whims at every opportunity. Being attractive in his youth, he was popular with women both highborn and lowborn. He had as many as nine mistresses and many bastards. Supposedly, he had any woman he wanted whether they were married or not. People often joked that while the Targaryen words were "Fire and Blood", Aegon IV's motto might as well have been "Wash her and bring her to my bed.".