Which character co-starred with John Steed in the first series of TV's 'The Avengers' in 1961?

The Avengers is an espionage British television series created in 1961. The Avengers initially focused on Dr. David Keel (Ian Hendry) and his assistant John Steed (Patrick Macnee). Ian Hendry left after the first series, and Patrick Macnee's John Steed became the main character, partnered with a succession of assistants. Steed's most famous assistants were intelligent, stylish and assertive women: Cathy Gale (Honor Blackman), Emma Peel (Diana Rigg), and Tara King (Linda Thorson). The Avengers ran from 1961 until 1969, screening as one-hour episodes its entire run. The pilot episode, "Hot Snow," aired on 7 January 1961. The final episode, "Bizarre," aired on 21 May 1969.

The Avengers was produced by Associated British Corporation, a contractor within the ITV network. After a merger in July 1968 ABC Television became Thames Television, which continued production of the series although it was still broadcast under the ABC name. By 1969 The Avengers was shown in more than 90 countries. ITV produced a sequel series The New Avengers (1976–1977) with Patrick Macnee returning as John Steed, and two new partners. In 2007 The Avengers was ranked #20 on TV Guide's Top Cult Shows Ever.

1962–64: Saw the appearance of Cathy Gale (Honor Blackman). Cathy Gale was replaced in 1965 – 1968 with Emma Peel (Diana Rigg). Emma Peel was replaced in 1968 – 69 with Tara King (Linda Thorson).