Originally Posted by cherokeesam
Or, here's a better interpretation:
They used the "known" properties of Extremis from Warren Ellis' book. There is only one "Extremis soldier" in Ellis' original --- namely, Mallen. The MCU ups the ante by creating a whole army of them. But comic-book Mallen had all the powers that MCU Killian had, including the fire breath.
So Black rewrote Extremis and had Killian assume Mallen's role, and infect himself with the virus instead of giving it to a white supremacist domestic terrorist. Killian's character in the movie is an amalgamation of Mallen, "real" Killian, and The Mandarin.
i see more of Mallen in Savin than Killian.