According to Marvel comics, Sentinels are a group of super-powered machines, designed to terminate mutants. As such, they majorly serve as antagonists to the X-Men across all formats. The Sentinels made their big-screen debut through 2014’s X-Men: Days of Future Past, which saw Peter Dinklage’s Bolivar Trask conceptualize their invention.

Robert Downey Jr. has shared a new behind-the-scenes photo from the set of Avengers: Doomsday – and eagle-eyed fans have spotted a detail that might reveal something about his Doctor Doom costume.