An arc reactor is a fictional power source from the Marvel Comics universe, primarily associated with the character Tony Stark, also known as Iron Man. It is depicted as a compact, clean energy generator that provides immense power, enabling Stark's advanced technology and his armored suit's functionality. In the storyline, the arc reactor was initially created to keep shrapnel from reaching Stark's heart after a life-threatening injury. Over time, it evolves into a symbol of innovation and sustainability, representing Stark's commitment to using technology for good while combating various threats.