Action icon Sylvester Stallone has joined the cast of The Suicide Squad confirmed filmmaker James Gunn. Gunn posted a picture on Instagram, where he is posing with Stallone. The two are looking at the camera and smiling. "Always love working with my friend @officialslystallone & our work today on #TheSuicideSquad was no exception. Despite Sly being an iconic movie star, most people still don't have any idea what an amazing actor this guy is," Gunn captioned it.