The former Kingsguard to Aerys II Targaryen, Ser Barristan Selmy served Daenerys Targaryen as one of her top advisors. He'd dole out pieces of advice if she was faced with conundrums. This particular time in Game of Thrones season 5, episode 2 "The House of Black and White," Ser Barristan suggests Daenerys give the Sons of the Harpy a fair trial to show the people of Meereen she is better than those who seek to depose her. However, a freed Meereenese slave, Mossador suggests otherwise, and Daenerys dismisses her advisors. Ser Barristan stays: "Your Grace? A word, please, I beg you... about your father. About the Mad King." He goes on to say that the Mad King earned his name: "When the people rose in revolt against him, your father set their towns and castles aflame. He murdered sons in front of their fathers. He burned men alive with wildfire and laughed as they screamed."

Ser Barristan's words leave a deep impact on Daenerys, and she agrees not to have the Son of the Harpy executed without a fair trial. Game of Thrones is laced with quotes and recollections of characters who survived the Mad King's wrath. Aerys II's devolution is a matter of fact. He criminalized peaceful dissent in the realm and inflicted atrocities on those who dared to speak against him.

Related

Game of Thrones: What Happened To Widow's Wail After Joffrey's Death?

Widow's Wail was among the two swords reforged from House Stark's Ice, but what happened to it after Joffrey's death in Game of Thrones?

Aerys II Targaryen Ascends The Throne

Aerys II's reign began on a good note, and he helmed the greatest dynasty of Westeros for a brief. Unfortunately for him, he could escape the mental disorders caused by generations of inbreeding in House Targaryen. It is a well-known fact that the Targaryens wed brothers and sisters for hundreds of years to keep the bloodlines pure and to centralize power within the family. Aerys II and his sister, Rhaella were married in the tradition of House Targaryen, and she bore him three children viz, Rhaegar, Viserys, and Daenerys who lived to adulthood.

Aerys II began his reign by replacing old lords at his court with promising younger men. Lord Hand Tywin Lannister, whom he befriended during his early years was one such example. By the time he ascended the throne in 262 AC, his sister-wife, Rhaella had already given birth to their firstborn son Prince Rhaegar. Aerys gradually succumbed to Targaryen madness, and he showed signs of paranoid schizophrenia with time. Whilst deterioration in Aerys' mental state first and foremost is attributed to inbreeding, Rhaella's miscarriages, stillbirths, and the deaths of their children were contributing factors. Aerys concluded that none of these children were his and that his sister-wife, Rhaella had been an unfaithful wife. She remained confined within Maegor's Holdfast at his orders and had two Septas keep an eye on her. Furthermore, Aerys' strained relationship with Tywin and the event of the Defiance of Duskendale worsened his mental health.

The Mad King's Grandiose Plans

While the Mad King wanted to be seen as the greatest in the history of the Seven Kingdoms, it was he who brought about the near end of House Targaryen. Initially, he was actively involved in politico-administrative decisions of the Seven Kingdoms but abandoned his plans due to the collapse of interest.

All of Aerys' plans and schemes were capricious, eccentric, and grandiose. The realm didn't see an immediate need to extend the Wall further North or to build a war fleet to "bring the Titan to its knees" after disputing with the Iron Bank of Braavos. More of his eccentric plans included the talk of invading the Stepstones, the construction of a white marble city on the south of the Blackwater Rush, and building an underwater canal under the deserts of Dorne.

The ideas and visions that Aerys II had for the realm would have inflicted a living crisis on his subjects, but thankfully they remained unexecuted. The cause of prosperity in Aerys' realm was in part due to his Lord Hand, who settled the dispute with Braavos and won the support of the lords, elites, and merchants in the Seven Kingdoms. He was responsible for the welfare of the realm, and many thought of him as the real ruler. Needless to say, Aerys resented Tywin's mettle.

Muting A Knight, Burning People, And Paranoia

Aerys' inhuman treatment of his critics includes tearing out the tongue of Tywin's captain of the guard, Ser Ilyn Payne, blaming his newborn, Jaehaerys' death upon his wetnurse, and executing her. He grew increasingly paranoid about Viserys' safety to the point the prince's mother wasn't allowed to be with him. He has his Kingsguard watch over him day and night. After the Defiance of Duskendale, he confined himself to the Red Keep for four years. The event refers to Aerys' imprisonment at the port of Duskendale and subsequently imprisoned by Denys Darklyn for refusing to pay attention to his people's welfare. This marked a turning point in Aerys' life, and he was never the same again.

By the end, he didn't even feel safe around his Hand, Tywin, and distrusted his heir, Rhaegar. He appointed Varys as master of whisperers on the small council because he'd about him. He saw assassination attempts everywhere and grew an unhealthy obsession with fire, and wildfire. The pyromancers of King's Landing greatly prospered under him, and he resorted to executing people using wildfire. He named Tywin's son, Jaime to the Kingsguard to keep the latter close and use him as hostage. The court was divided between those who showed Aerys unwavering loyalty and Prince Rhaegar's faction of reasonable men. The Tourney at Harrenhal appalled Aerys' subjects. Due to his fear of blades after Duskendale, he willingly chose to grow his beard and nails. Unclean, unshaven, and unkempt after the Defiance of Duskendale, and unhealthy due to fear and paranoia, Aerys didn't look regal by any stretch of the imagination.

Robert's Rebellion

Lyanna and Rhaegar's romance and Aerys' executions of Lord Rickard Stark and his heir, Brandon, was the final nail in the coffin. When Brandon and his companions demanded the safe return of Lyanna Stark, Aerys had them arrested for treason and summoned their fathers to King's Landing. Lord Rickard Stark demanded Trial by Combat, and Aerys declared Wildfire the champion of House Targaryen. He burned the Warden of the North with Wildfire and watched as Brandon struggled to free his father with a noose around his neck. As Aerys demanded the heads of Jon Arryn's wards, Ned and Robert, the stage for ripe for a civil war.

In the last leg of Robert's Rebellion, Aerys let Tywin through the city's gates at Pycelle's counsel, and as the Lannister men began sacking the city, he demanded Jaime bring him Tywin's head. Aerys' final solution was to set fire to the caches of Wildfire that he placed all over King's Landing. His final words, as heard on Game of Thrones were: "Burn them all!"

To prevent the catastrophe, Jaime shoved his sword in Aerys' back and watched as he bled to his death. He later recalled the incident to Brienne of Tarth: "Aerys saw traitors everywhere, so he had his pyromancers place caches of wildfire all over the city. Beneath the Sept of Baelor and the slums of Flea Bottom. Under houses, stables, taverns. Even beneath the Red Keep itself!"

MORE: Game Of Thrones: The History Of Oathkeeper, Explained