Robert Mitchum was an American actor who was in over 110 films and TV series over the course of his career.
 He is ranked as #23 on the American Film Institute's list of the 50 greatest American screen legends of all time.
 His first credited named role was as Quinn in the 1943 film "Border Patrol".
 That same year he appeared in the films "Follow the Band", "Beyond the Last Frontier", "Cry 'Havoc'" and "Gung Ho!
" as well as several Hopalong Cassidy films including "Colt Comrades", "Bar 20", "False Colors", and "Riders of the Deadline".
 In 1944, he starred in the western film "Nevada" as Jim Lacy aka Nevada and a year later in the film "West of the Pecos" as Pecos Smith.
 During the 1940s, he also cast in the films "Undercurrent" (1946), "Crossfire" (1947), "Out of the Past" (1947) and "The Big Steal" (1949).
Hopalong Cassidy or Hop-along Cassidy is a fictional cowboy hero created in 1904 by the author Clarence E. Mulford, who wrote a series of popular short stories and many novels based on the character.
Lewis J. Rachmil (July 3, 1908 – February 19, 1984) was an American film producer and art director.
 He was nominated for an Academy Award in the category Best Art Direction for the film "Our Town".
 In the mid and late 1940s, he produced several of William Boyd's popular "Hopalong Cassidy" B-Westerns.
 In 1959, he was producer of "Men into Space," a one-season CBS TV series that tried to give a serious science fiction preview of where the then-new American space program seemed to be heading.
 During the 1960s he produced several films in England for Mirisch Films.
Callaway Went Thataway is a 1951 American comedy film starring Fred MacMurray, Dorothy McGuire, and Howard Keel.
 It was written, directed, and produced by Melvin Frank and Norman Panama.
 Also known as The Star Said No, it was a satire of the television program "Hopalong Cassidy".
In United States films of the Western genre between the 1920s and the 1940s, white hats were often worn by heroes and black hats by villains to symbolize the contrast in good versus evil.
 The 1903 short film "The Great Train Robbery" was the first to apply this convention.
 Two exceptions to the convention were portrayals by William Boyd (active 1918–1954), who wore dark clothing as Hopalong Cassidy, and Robert Taylor's portrayal in the film "The Law and Jake Wade" (1958).
Stagecoach War is a 1940 American Western film directed by Lesley Selander and written by Norman Houston and Harry F. Olmsted.
 The film stars William Boyd, Russell Hayden, Julie Carter, Harvey Stephens, J. Farrell MacDonald, Britt Wood and Rad Robinson.
 The film was released on July 12, 1940, by Paramount Pictures.
Hop-Along Cassidy is a 1935 American western film, featuring the character "Hop-Along Cassidy" created by writer Clarence E. Mulford.
 This is the first of 66 "Hopalong Cassidy" films produced between 1935 and 1948 and all starring William Boyd in the title role.
 William Boyd was originally offered the role of Buck Peters, the ranch foreman, but decided to take the role of Hop-Along instead.
Richard Percy Jones (February 25, 1927 – July 7, 2014), known as Dick Jones or Dickie Jones, was an American actor and singer who achieved success as a child performer and as a young adult, especially in B-Westerns.
 In 1938, he played Artimer "Artie" Peters, nephew of Buck Peters, in the Hopalong Cassidy film, "The Frontiersman".
 He may be best known as the voice of Pinocchio in the 1940 second Walt Disney film of the same name.
Hopalong Cassidy, also known as Hop-along Cassidy, is a fictional cowboy hero created in 1904 by author Clarence E. Mulford who has appeared in a variety of media.
William Lawrence Boyd (June 5, 1895 – September 12, 1972) was an American film actor known for portraying the cowboy hero Hopalong Cassidy.

Question: What genre was the 1940 film starring an American film actor known for portaying the cowboy hero Hopalong Cassidy?
Answer: Western