Hansen wrote nearly 40 books in a variety of genres, but was best known for his Dave Brandstetter mystery-novels (starting with Fadeout in 1970). Brandstetter lasted for a total of twelve books spanning 21 years and was the first tough, hardboiled, no-nonsense detective who just happened to be homosexual. Hansen also wrote a series of short stories about Hack Bohannon, a combination private eye and horse-ranch-owner in central California.