If never heard of Donald Hamilton, don't feel bad. You're not alone. Even those who've seen the movies with Dean Martin may not realize that Hamilton's Matt Helm is not a flip pretty-boy superspy, but a grim agent doing a dirty job. This well written and exciting series predated the James Bond-inspired spy mania of the mid-60s and provides an important link between the paperback originals of the 50s and the paperback series of the 70s and 80s - series with names like The Executioner and The Destroyer. In addition, he wrote other crime fiction, as well as a number of excellent westerns.
In Hamilton's world, Helm is a skilled outdoorsman, cool under pressure, a consummate killer. As the first novel opens, he's retired from the spy trade to settle down, and he's married and started a family. His past, of course, won't leave him alone, and when it threatens his new life he finds his old skills are still sharp as ever. In saving his new life, however, he ends up destroying it; he's unable to reconcile his bloody history with his new family life, and again becomes a professional agent.
The only explanations for the rather poor movies are a) they were designed to catch the post-James Bond comedy spy craze, and b) they were intended purely as star vehicles for Dean Martin and so played to his established on-screen persona. None of the movies are particularly worth watching, despite the fact that two of them were (ahem) helmed by veteran noir director Phil Karlson.
Other Books The Mona Intercept (1980)
Buy Assignment: Murder (1956) aka Assassins Have Starry Eyes Line Of Fire (1955) Rough Company (1954) Night Walker (1954) The Steel Mirror (1948) Date With Darkness (1947)