The 20-year-old actor - who plays young tyrant Joffrey Baratheon - told GQ that he is strongly influenced by classic film and TV villains.
"It's something that's so easy to slip into because I've seen so many villainous characters on TV and on-stage and in films," he explained. "Joffrey is definitely informed by those performances."
Gleeson added that Joaquin Phoenix's performance as Emperor Commodus in 2000 film Gladiator was a "big influence" on his portrayal of Joffrey.
"Sometimes when I'm sitting on my throne, I think of Phoenix sitting on his, with that smirk on his face," he admitted.
The star also suggested that Joffrey has been "made bad" by his family and the situations he finds himself in.
He claimed: "With Joffrey, the evil and malicious things he does are by-products of the setting that he's been brought up in, how his family behaves, and what he's been made to believe of himself."
Game of Thrones airs on HBO in the US and on Sky Atlantic in the UK. A third season will premiere in April 2013.
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Watch a recap of the Game of Thrones season two finale below: