The Arc Reactor is a power source designed by Howard Stark, Anton Vanko and Obadiah Stane to replicate the Tesseract's energy. After the Tesseract's energy had been harnessed by HYDRA during World War II, Stark studied the Tesseract attempting to do the same. Limited by the technology at his disposal, Stark and Vanko used his research on the Tesseract to create the Arc Reactor. Intended to be the first stage of Project P.E.G.A.S.U.S., the Arc Reactor remained generally inactive until Tony Stark was able to miniaturize it and power his Iron Man armors.