"Father" is the codename given to a blind female British government official who appears as a supporting character in the 1998 film The Avengers, based on a very brief appearance in the British TV series of the same name.
She can be regarded as a foil for "Mother," a wheelchair-using male British government official who gives orders to the main characters in the last season of the series and in the film. The humorous use of "Mother" for a male character is the source of the use of "Father" for a female character. In the original series, "Father" is portrayed by Iris Russell; in the film, she is portrayed by Fiona Shaw.
"Father" only appears in a single episode ("Stay Tuned") in the final season of the original series, where she is a very minor character, introduced mainly because actor Patrick Newell, who portrayed "Mother," was not available due to scheduling conflicts. Although her appearance in the TV series is exceedingly brief, it does make clear that she compensates for her blindness by the exceptional acuteness of her hearing (an ability that is also apparent, though never explained, in the film).
In the film, the character of "Father" gets considerably more screen time. She initially does not seem very important; she is simply a higher official, whereas "Mother" is the direct authority over John Steed (portrayed by Ralph Fiennes) and Emma Peel (portrayed by Uma Thurman). Her importance to the plot becomes obvious near the end of the movie, when it is revealed that she is a traitor in league with the villain, Sir August de Wynter (portrayed by Sean Connery).