Dr. Sienna Brooks

Dr. Sienna Brooks is the hidden true main antagonist of the Dan Brown novel Inferno and the film adaptation of the same name. She was the lover of Bertrand Zobrist and plans to carry out his work by releasing his virus upon humanity. She was portrayed by Felicity Jones in the film, who is also best known for her roles as Felicia Hardy, Jyn Erso and Jane Hawking.

Inferno
Sienna is first introduced when she begins some medical work on Robert Langdon who was in a coma due to him having amnesia when he wakes up in her hospital room. When another agent for the Consortium named Vayentha comes in and supposedly killed Brooks' partner Dr. Marconi on her path to killing Langdon, Sienna fled the hospital with Langdon. She later discovers along with Langdon that he was the one who stole Dante Alighieri's Inferno mask which was once a belonging to a man named Bertrand Zobrist.

Their quest takes them to a set of clues which brings them to Venice and then it was discovered that the last clue was in Istanbul which gave them evidence that a virus was to be unleashed upon the world.

However, knowing that Zobrist had set the date to when the virus was to be released, it couldn't ever be stopped.

Sienna betrays Langdon and tells him that she was his girlfriend at the time before his death. She also tells him about a letter that was sent to her about the Inferno portion of the plan. She said that if the WHO got a hold of the virus, that the organization would use the technology for weaponry. So she managed to apprehend it before anyone else could take it.

After this, Langdon manages to stop her by asking her to trust him and that she was the only one who could stop Inferno and that the world needed her.

When she told everything she knew about Inferno to Dr. Elizabeth Sinskey, she was sure Sienna could be crucial to a meeting for a meeting in Geneva. Langdon and Sienna said goodbye afterwards.

In the film version, Sienna is defeated as she managed to commit suicide to ensure that the virus would be released