Rhaegal was one of the dragons born on the Dothraki Sea, along with Drogon and Viserion. Commanded by Daenerys Targaryen, he was named for her brother, Rhaegar Targaryen. Rhaegal was the first dragon in a century to touch Westerosi soil after Daenerys landed upon the shores of the Crownlands. Of the three beasts, Rhaegal seemed to be the most eager to breath fire upon Daenerys' enemies, and seemed most fond of her son, Maekar Targaryen.
Rhaegal has green and bronze scales. His green scales are a dark green, the green of moss in the deep woods at dusk, just before the light fades, and they gleam like jade. His teeth and claws are black. His eyes are bronze, brighter than polished shields, and they glow with their own heat. His flame is orange-and-yellow fire shot through with veins of green.
Like his two brothers, Rhaegal flew overhead as Daenerys assaulted King's Landing with all her draconic might. While Daenerys rode Drogon, Rhaegal flew over the Golden Company's ranks, burning anything he found. Elephants and siege weapons and men burnt alike that day, and by the time they had retreated in the evening, the Golden Company had taken massive losses, leading to Aegon Targaryen's exile back to Essos.
Rhaegal was later ridden by Daenerys' Son, Maekar, whom possessed an ability to befriend dragons from a young age. During the Third Greyjoy Rebellion, Rhaegal was ridden by him. Rhaegal and Maekar both met their end in Pyke after an iron bolt went through his eye, supposedly fired by Joseran Volmark.
Daenerys Targaryen was forced to retreat and muster her forces once more, the death of one of her dragons leading to vassal mistrust as they learned that dragons were, indeed, mortal. The loss of her son amongst her dragon was a special hit to the Queen, leaving her essentially heirless for a time.
Rhaegal's body was retrieved after Daenerys Targaryen won the war, and thus his skull was put amongst those of his predecessors. Rhaegal's slayer was executed in 367AC.