The 35-year-old revealed that he finds it difficult to relate to Elijah, admitting that some of the vampire's decisions have been questionable.
"I think that he's an idiot," Gillies told Assignment X. "Some of the things that [Elijah has] done, especially toward the end of last season, I was like, 'Well, that's obscenely ridiculous'."
He explained: "There was no way that anybody that intelligent, who'd been alive that long, who can murder another vampire, no less, with the back of his hand, who can move faster than light, is going to go, 'You know what? This guy [Klaus] is not so bad…'
"And I love you [producer] Julie [Plec], I love you [producer] Kevin [Williamson], but I thought that was just… odd."
Gillies went on to say that he thinks Elijah is capable of forgiving Klaus (Joseph Morgan).
"I think if he returned the family to Elijah and if he left Elena alone, [Elijah would forgive him]," he said.
Vampire Diaries star Claire Holt recently teased that viewers will discover more about the Originals on the next episode of the CW series.
The Vampire Diaries airs on Thursdays at 8/7c on The CW in the US and on Tuesdays at 9pm on ITV2 in the UK.
> The Vampire Diaries: 'Ordinary People' in pictures