The title refers to Margaret Thatcher, who was Prime Minister of Britain from 1979 to 1990. She was, and still is, Britain's only female PM, and was known as the Iron Lady because of her inflexible character and determination, and her reputation for being ruthless. The film has annoyed some Thatcher supporters (mainly in her own Conservative party) either because they feel the film should have been made after her death or because they think it attacks her policies. Thatcher does tend to split opinions; people in the UK either supported her strongly or really detested her.

Baroness Thatcher is still alive but now suffering from dementia, which the film shows. There is disagreement over how accurate the movie is - there certainly are some historical errors, but the main focus is on her as a pioneering female politician. One thing everyone agrees on is that Meryl Streep's performance as the Iron Lady is amazing.