Here's why Drogon destroyed the Iron Throne in the Game of Thrones series finale. The black dragon was the lone remaining beast belonging to Daenerys Targaryen and he was her loyal companion since he was born in the Game of Thrones season 1 finale. However, Drogon's strange behavior before he vanished in "The Iron Throne" remains puzzling for many.
In the Game of Thrones series finale, "The Iron Throne", Daenerys rode Drogon back to King's Landing for her victory speech before her loyal Dothraki and Unsullied armies. Later, a sleeping Drogon stood guard over the entrance to the Red Keep but he allowed Jon Snow to enter. Tyrion Lannister, who was imprisoned and sentenced to die for treason, urged Jon to "save" Westeros from the dictator Daenerys had become. Finding her in the demolished throne room of the Red Keep, Jon stabbed Dany and murdered her. Somehow, Drogon sensed his mother was in danger and he flew into the throne room to confront Jon.
Naturally, Jon fully expected Drogon to avenge his mother and burn Jon Snow to death. Instead, after he gently prodded Daenerys' body, Drogon reared back and unleashed his dragonfire on the Iron Throne. When the ancient chair was finally melted, Drogon took Daenerys' body in his claws and flew across the Narrow Sea. But why did the dragon destroy the Iron Throne and not Jon Snow?
It must be said that Drogon has always liked Jon Snow; in Game of Thrones season 7, the dragon seemed to sense the truth about the bastard of Winterfell - that he's half-Targaryen. Drogon's friendliness to Jon is one of the reasons Daenerys began to trust him. It's possible that this shared connection between the two meant that Drogon felt he couldn't avenge his mother's death directly, instead taking his anger out on the Iron Throne. Some could also argue that, as Drogon didn't see Jon kill Daenerys, he didn't make the automatic assumption that it was Jon who killed her, thus sparing his life.
Drogon's decision to attack the Iron Throne is thus a letting out of his anger, directed at the political structure that so obsessed Daenerys and had driven her to become the Mad Queen; perhaps even making a statement that if Daenerys can't have the Iron Throne, no one can. It also saw, even in death, Dany inadvertently help achieve her dream to "break the wheel". Drogon melting the Iron Throne thus symbolized the ending of that era of Westeros, which was begun 300 years ago by Daenerys' ancestor Aegon the Conqueror. Since it was Aegon's black dragon Balerion who forged the Iron Throne with his dragonfire, it's fitting that Daenerys' dragon would destroy it centuries later.
Like so much of how Game of Thrones season 8 was plotted, this seemed like an act of expediency for the sake of the story. And yet - as with Drogon flying his Queen out East - it's heavy in symbolism and deeper meaning.