Extradimensional beings Cyttorak, Ikonn, Valtorr, Krakkan, Balthakk, Watoomb, Raggadorr and Farallah were in dispute as to which of them was the most powerful. They agreed to a wager that each one of them would have their followers on Earth build them a temple and they'd place an artifact within it that housed a portion of their power. Eventually humans would be drawn to these artifacts and be empowered by them and then together they'd build the God Machine. The Machine would drain humanity of their free will and the eight Exemplars would each lead one eighth of the world's population into battle until only one remained.
Juggernaut was the first Exemplar, empowered by the Crimson Gem of Cyttorak located within a temple in Korea. The activation of one Exemplar was supposed to cause others to be drawn to the other temples. However, the temple in Korea was being bombed when the Juggernaut was activated and this disrupted the summoning spell.
It wasn't until years later when the temple of Balthakk was discovered in Nunavut the summoning spell was activated. Charter pilot Samantha McGee was hired to fly Tony Stark to the archaeological dig and she found herself drawn to the Blinding Brazier of Balthakk and became Inferno. With Inferno activated the summoning spell was finally sent out and others were drawn to the other temples around the world.