Marvel Studios launched the most successful film franchise in history with four of the world’s most recognizable faces, the director of Elf, and a $140 million budget. 2008’s Iron Man was by no means a Cinderella story, but the fire-engine red and gold hero was not a guaranteed box-office juggernaut. Twelve years later, it’s easy to retrace the studio’s journey behind a charismatic star, a perceptive producer, and its beloved universe of characters.