* Tony Stark (A.K.A Ironman, owner of Stark Industries) was attacked after a military missile presentation and was taken away by terrorists. Due to the blast near him he got fine metal scraps in his body which could flow into his heart and would kill him

* Now, the terrorist wants Tony Stark to build them weapons. So, they get a doctor to fit an electromagnet in Tony Stark’s chest to keep those scraps from flowing into his heart. The electromagnet is connected to a battery, this requires Tony to carry that heavy battery everywhere.

* To solve this problem, Tony Stark builds himself an miniaturized Arc Reactor (a small but highly durable power source) to run his electromagnet. He then inserts that Arc Reactor in a cavity on his chest. Later, Tony uses this Arc Reactor’s enormous energy to power his armor suits (we call Ironman)

* Much later (in Ironman 3), Tony Stark finally gets those metal scraps out of his body, through an operating. Now he uses Arc Reactors only to power his suits. He doesn’t have Arc Reactor in his chest anymore but all his suits have them inbuilt.

Unlimited power