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...I had a thought that would guide me for years to come. Anonymity, Tony. Thanks to you, it's been my mantra ever since, right? You simply rule from behind the scenes. Because the second you give evil a face, a Bin Laden, a Gaddafi, a Mandarin, you hand the people a target.
~ Killain confessing his plans behind the bombings to Tony Stark held captive.
Aldrich Killian is the true main antagonist of Iron Man 3. He adopted the identity of the "Mandarin" as his own.
He is portrayed by Guy Pearce.
In 1999, Aldrich Killian initially asked for Tony Stark's support for his project under Advanced Idea Mechanics, only to be shunned and ignored by the latter. After realization that Tony had ignored his proposition, Killian decided to work on his own in creating an expansive business for himself.
Over the years, through his privately funded organization A.I.M., Aldrich Killian created a team to further research and develop the Extremis virus, which imparts unusual levels of strength and resiliency to human subjects.
Iron Man 3
After curing himself of his disability by using a dose of his own Extremis virus, he orchestrated many terrorist attacks as part of his experiments, while creating a false Mandarin person through the use of an actor, to mask his illegal activities. He orchestrates the attack at Tony's home, kidnapping Pepper Potts afterwards. Having Pepper Potts as his "trophy" and hostage, he injected her with the Extremis virus to further motivate and antagonize Tony.
After his men had abducted President Ellis, Killian had planned to orchestrate a live feed showing the murder of Ellis, only for Tony Stark and James Rhodes to interrupt and attack their base with the help of Tony's J.A.R.V.I.S.-controlled Iron Man suits. In the ensuing battle, Tony finally finds Pepper, only for her to be trapped under debris. Before he is able to rescue her, an angry Killian attacks Tony with Tony distracting Killian to rescue Pepper.
While Pepper seemingly dies after falling to her apparent death, Killian approaches Tony for a one-on-one battle. The two engage in a brutal and epic final fight with Tony switching between various Iron Man suits as Killian destroys each one after another. As Tony was unable to attach any more extra armor onto himself, JARVIS sent the Mark 42 prototype to aid Tony in his battle. Tony then kinetically attached the armor onto Killian to stall his movements. Tony then activated the Mark 42's self-destruct function attempting to destroy Killian in the process.
After the complex in which the two were fighting was demolished, the battered Tony is confronted by Killian who is shown as surviving the explosion due to the Extremis virus that he created and took. Approaching Tony, he elaborates upon the revelation that he is the real Mandarin and that the two should stop "wearing masks" to hide their identities. Just before he is able to attack Tony, Pepper attacks him from behind, having survived her fall with the help of her new found Extremis abilities. Just before Killian is able to retaliate, Pepper rips an arm from one of the stray Iron Man suits, attaching it to her herself and utilizing its capabilities to finally kill Killian for good.
The revelation that Aldrich Killian is in fact "The Mandarin" as well as the main antagonist of Iron Man 3 is similar to the twist in the DC Comics film Batman Begins in regards to its principal antagonist known as Ra's Al Ghul. Both characters employed a double to disguise their true identities in order to avoid exposing themselves; with the difference being that Killian had hired Trevor to act out an idealized appearance of "The Mandarin" to divert the media and Tony Stark's attention away from his illegal activities, while the real Ra's Al Ghul had implemented the use of a decoy to protect and disguise himself as the mentor of Bruce Wayne. Ironically, both characters were portrayed as being of caucasian descent in their respective film versions (at least based on the ethnicity of their actors), despite both of the comic versions of the Mandarin and Ra's Al Ghul being originally inspired by the "Fu Manchu" stereotype. Also, Guy Pearce was considered to portray Ra's Al Ghul in Batman Begins, but the part ultimately went to Liam Neeson.
This interpretation of the Mandarin seems heavily inspired by the comic Iron Man: Director of SHIELD (#15-28). Within the comic, not only does the Mandarin attempt to use Extremis-enhanced soldiers as a part of his plan to cleanse humanity, but he is also depicted as fighting shirtless during his battle against Iron Man, much like how he is depicted in Iron Man 3.
In the comics, the Mandarin and Aldrich Killian are separate characters and Aldrich Killian was a very minor one-time character who committed suicide after he let a group of terrorists led by Mallen get ahold of the Extremis virus. Killian was also initially thought to be the sole conspirator before it was revealed that Maya Hansen was the mastermind in a plot to pit the Extremis Virus against Iron Man to renew their military funding after the army cut them off.
Killain's and Tony's past story was also an exact match to the main plot thread of Pixar's film The Incredibles, with Killain's story being similar to Syndrome's.
He is similar in appearance to Edward Nygma/The Riddler in Batman Forever, both before and after becoming a supervillain. In addition, both went ahead with a project rejected by the main protagonist.
He is the second Iron Man villain to be killed by Pepper after surviving a fight with Iron Man, the first being Obadiah Stane.
In the comics, his powers match a villain called Firebrand. However, he was not reffered that anywhere in the movie.
Killian can be considered the MCU's version of The Mandarin.