Newly released early animatics for Iron Man 3
reveal a few changes to scenes that we see in the film. A few major ones include Trevor dying in an Extremis-induced explosion at the docks in the finale of the film (in "Finale Part I")...and a final battle with a character named Kreiger, who Tony encapsulates in the Mark 42 and blows up (in "Finale Mark 42 Rescue")...
Obviously, this is the exact scenario that plays out between Tony and Killian in the final film. It seems safe to say that Killian's character actually replaced Kreiger in later versions of the script... So who is Kreiger?
Well, the only "Kreiger" I could find mention of in Marvel lore is Simon Krieger (minor spelling difference in the last name). Simon was the Vice President of "Republic Oil & Natural Gas", which eventually became Roxxon Oil Corporation. He and several other Republic Oil board members were responsible for Tony's parent's deaths in the midst of a bid to take over Stark Industries. Krieger himself disguised himself as Tony Stark at one point in an attempt to ruin Tony's reputation, but was foiled by Happy Hogan.
The use of Krieger as the main villian of the film is a baffling choice, which the creators of the film clearly came to recognize as they replaced him with Killian: a villain with clear comic ties to Extremis. Of course, Krieger's initial role makes the use of the Oil Tanker dock finale and the frequent Roxxon Oil references in the film far more understandable.
But then there's the question of whether or not Krieger would have ultimately revealed himself to be the true Mandarin as Killian did. If not...that would have meant that there would have been no "real" Mandarin in the film at all; only a portrayal of the Mandarin by Trevor.