Infernal is one of the signature heroes of City of Heroes
Infernal is a native of an alternate dimension, "Infernal Earth", which is overrun by demons. He was the most skilled of his order at binding demons into his armor, which gives him his power. He was undone by his best friend T'Keron, who grew jealous of his ability. T'Keron attempted to bind Valmaz, Lord of Demons, but managed to not only merge himself and Valmaz, but pull the three of them into a portal to our Earth. While still adjusting to our world, he continues his search for T'Keron and Valmaz.
Recently Lilitu, Infernal's mother, showed herself to be an agent of the Circle of Thorns, and appears to be an extremely powerful succubus. It's unclear how exactly she came to be on this Earth, unless the Circle went looking for her specifically.