While HBO's ongoing prequel House of the Dragon delves into House Targaryen's history more than elsewhere on TV, King Aerys II Targaryen — depicted in Game of Thrones — is one of Westeros' most important and infamous figures. He was portrayed in the flagship TV show by Liam Burke and David Rintoul in brief flashback sequences.
Source:https://www.cbr.com/hbo-game-of-thrones-mad-king-name-explained/