There was once a king of the Inhumans, who ruled justly. However, he stole the Slave Engine, his people's greatest weapon, along with the Xerogen crystals it utilized and buried them somewhere in Tibet, for fear that it would corrupt his people. This led to a duel between himself and the heir to the throne, young Blackagar Boltagon. Despite being by far the strongest of the Inhumans, moving the Slave Engine had weakened the Unspoken which led to his defeat at the hands of Blackagar and his friends. His final stipulation was that his deeds be remembered, but Black Bolt had a crueler fate in mind: the King, his deeds, and the Slave Engine itself, were written out of Inhuman history. From that day, he would be remembered only as a bogeyman to frighten small children. He would be... Unspoken.
He was later recovered by the Alpha Primitives, who cared for their fallen king. Realizing his mistake, the Unspoken plotted to return and reclaim his throne, cultivating the Xerogen crystals, only for Attilan to rise into the sky. Cheated of his redemption and later learning of the Silent War between the Inhumans and United States of America, the Unspoken decided to change his plans and conquer Earth, unearthing the Slave Engine and planned on transforming all humans on the planet into Alpha Primitives.
In the 21st century, the Unspoken was detected in Tibet. G.R.A.M.P.A. interpreted this as a possible alliance between communist China and the Inhumans but were unable to identify the Unspoken. Therefore, they called in Quicksilver, an expert on the Inhumans, and U.S. Agent.
The former recognized the Unspoken and advised that they call all the Avengers teams to stop him. Unfortunately, even the joint forces of the New Avengers, Avengers Resistance and Mighty Avengers failed to stem the tide. Most of their force were mutated by the Xerogen mists, before the Wasp arrived. They both dueled each other at massive sizes. Wasp called him pathetic, for wallowing in his own misery for his own mistakes and not learning to move on.
The Unspoken was defeated when the chronal ray onboard the Slave Engine that accelerated the growth of the Xerogen crystals was used against him, aging him to the point where he was too weak to carry on fighting. The heroes then allowed the Alpha Primitives to allow the Unspoken to return to his cave to live out the rest of his days.
The Unspoken is the living embodiment of Terrigenesis itself. He is capable of anything, including increasing in mass and conjuring up energy swords.
Stronger than anyone on Earth.
The Unspoken's status as inherently stronger than the King of the Inhumans plays to myths about the Titans, the predecessors of the Greek gods, who were considered even more powerful than their successors.