Another series of excellent forgotten books is the Matt Helm series by US author Donald Hamilton. The 20-plus books cycle the adventures of a killer in the services of a black-ops problem solving unit. I like them for several reasons, that's why I aspired to emulate some of the elements in "Troubleshooter":

A ruthless hero - Matt is uncompromisingly focussed on the success of his missions, killing another agent (foreign or own) is just a collateral damage for an otherwise very sympathetic hero. In one of the books there is a nice scene where Matt runs off a foreign agent from the road, resulting in a devastating car crash for the other agent. Matt drives on without helping to continue the mission. Another agency in pursuit of them stops to help the foreign agent in his car wreck—instead of following the mission protocol—and promptly gets killed. (Soft gets you killed in this job)
Independence - In the early books Matt still has a family but has this secret agent / killer past. After that breaks down, he basically moves through the adventures alone, occasionally a fellow agent at his side, but most repeating characters are killed off after a few adventures. Plan is to give Paul Trouble a reverse journey—from loner to social human being—in the following books.
Clear right and wrong - Donald Hamilton's spy novels play during the cold war area where things were black and white: red = bad, USA = good.