Stallone stars in Bullet to the Head as a hitman who is brought together with a Washington DC detective (Sung Kang) by two murders.
Speaking to Flicks and Bits, the actor explained that he was drawn to the contradictions of his character Jimmy Bobo.
"I like the morality of it, that the guy still has an achilles heal," Stallone commented. "I like that he isn't flamboyant, he doesn't have an unbelievable amount of skill, he's not Rambo or that kind of thing. I also liked the sarcasm, and his dry humour – which I really liked."
He went on to say: "Jimmy Bobo's very at peace with himself. He plays by his own set of rules that are blunt but simple to follow. Jimmy believes he takes out the trash, he believes he removes those hard-to-get-out stains in society. He doesn't go after people who, in his mind, don't deserve it.
[Sylvester Stallone, Sarah Shahi, Sung Kang, Walter Hill and Jason Momoa at the 'Bullet to the Head' premiere]
"But now all of a sudden Jimmy's confronted with something he's never been confronted with before – a betrayal from within and a complete reliance upon a detective who hates his guts. Not exactly a strong support system."
Stallone also discussed working with director Walter Hill, who has had previous hits with 48 Hrs and Hard Times.
"[Working with Walter] was a relief and it was unexpected. I thought we were going to do 48 Hrs and other projects that I should have done, but I didn't," he said. "This film started to fall into the valley of trouble, and I thought, 'My God, this isn't going to go. This is going to go down in flames'."
The star further discussed championing Hill for the film: "It didn't work out with the previous director and it was becoming way too technical and visual, I wanted it to be old-school. So I said to the producers, 'Walter Hill?' And they said, 'He hasn't worked in a while'. So I said, 'Neither did I, for eleven years! The guys good'.
"He had the meeting and I think it brought out Walter's chops again. We had to do this on a tight budget, so I think what he got on film was a very entertaining, kind of a retro flashback with modern day technology. He really got his wings back. It felt good."
Bullet to the Head is now playing in the US and the UK. Watch a trailer below: