The hunky Hawaiian won legions of fans as the nomadic warrior king Khal Drogo in the hit fantasy series - but mainly spoke in an invented language.
As a result, when the 39-year-old's character was killed off at the end of season one, he struggled to get acting jobs.
"I didn't get much work after that," he tells U.K. chat show host Graham Norton. "I mean, what do you do with that - he (his character) doesn't speak English, he's not funny and he just hurts people. I played that character well so it was a bit challenging afterwards. People would literally say, 'Wow, you speak English!'."
Jason, who has two daughters, Lola Iolani, 11, and Nakoa-Wolf, 10, with fellow actress Lisa Bonet, confesses that his supposedly starmaking role left him struggling for money.
He explains: "2013 and I was literally broke - but the future would be bright! I couldn't say anything to anyone for years and I can't keep a secret to save my life. It was very hard for me so, I am glad we are now here."
Happily, he is now the star of D.C's superhero blockbuster "Aquaman" - but he has saved watching his biggest moment until he can do so with his kids.
"I have two babies aged 10 and 11," adds. "They were on set for the whole filming and they made me promise them that I wouldn't watch it until I can watch it with them. I want to share it with my children and sit and hold their hands - it's a rare moment for a father and generally, they can't watch the things I do!".
"Aquaman" is in cinemas now.