Karen Crowder is the main villain of Michael Clayton. She was played by Tilda Swinton.
Karen is U-North's general counsel and obtains Arthur's briefcase and discovers that he had come into possession of a confidential U-North document detailing the company's decision to manufacture a weed killer that it knew to be carcinogenic. Karen soon learns that Arthur has bipolar disorder and is unwilling to commit himself to a mental health institution. His psychotic episode was the result of his failing to take his medication. She decides to hire two men to follow him, including tapping his phone and installing bugs in his apartment. The surveillance collected eventually reveals that Arthur is building a case against his own client, leading Karen to ask the team to permanently incapacitate him. They assassinate Arthur in a manner designed to resemble suicide.
Michael is saddened by the news of Arthur's death, but becomes suspicious upon learning that U-North was planning a settlement just a few days before and that Arthur had booked a flight for one of the plaintiffs, Anna.He learns from Anna that she told no one of her conversations with Arthur, not even her attorney, arousing in Michael further suspicion about how his firm came to know of Arthur's conversations with the U-North class members. With the help of his brother-in-law in the police department Michael gets access to Arthur's sealed apartment and discovers a receipt from a copy store. Upon investigation, he discovers that Arthur had ordered three thousand copies of the confidential U-North document. Michael takes a copy with him, but the two hit men are tailing him and inform Karen of the situation. Michael is about to show his boss, Marty Bach, what he has discovered, only to be offered a renewal of his employment contract as well as an $80,000 bonus he had requested to cover his debt, although it comes with a confidentiality agreement to prevent him from ever shaking down the firm.
As Michael plays poker that evening, one of the hit men rigs his car with a bomb. Michael leaves the game and receives a phone call summoning him to the meeting with the client in Westchester County who had committed a hit-and-run, as seen at the start of the movie. He is being followed by the two men, but they have trouble tailing him. The surveillance team, still off but near Michael's trail, detonates the remote bomb while he is out of the car. An unharmed but surprised Michael runs back to his car and throws his personal effects inside, faking his own death.
Later, at a U-North board meeting, Karen proposes approval of a new settlement agreement. Michael is waiting for her when she exits the conference, and informs her that he has access to copies of the U-North memo and that he knows about her role in Arthur's murder. He goads Karen into offering him $10 million for his silence. Karen reluctantly agrees, prompting Michael to reveal the phone in his pocket that has conveyed their conversation to the police. As he walks away, detectives arrest Karen.