Interesting (and long) post on Spyderco’s blog:
The Spyderco Civilian is one of the most distinctive and instantly recognizable folding knives ever created. In addition to carving out its own place in history, it also inspired a number of derivative designs, all of which share its defining characteristic: a sinuous Reverse “S” blade shape. The story of this unique family of products represents a fascinating chapter in Spyderco’s history.
In 1981, Spyderco co-founder Sal Glesser single-handedly redefined the form of the modern folding knife. His dynamic combination of top-of-the-pocket clip carry and rapid one-handed opening with the Trademark Round Hole™ set a new standard in folder performance. The addition of a serrated edge a year later raised the bar yet again. Although these features are commonplace today, they set Spyderco knives well apart from the competition in the early 1980s. They also made them the preferred tools of savvy law enforcement personnel who valued them as both dependable working knives and potent backup weapons in officer-survival situations.
As a direct result of that dedicated law-enforcement following, in the late 1980s, Spyderco was approached by agents of a major U.S. federal law-enforcement agency with a request for a special-purpose folding knife. These agents specialized in undercover narcotics operations in which carrying a traditional sidearm—or even a backup pistol—was impossible. To improve their odds if a drug buy turned bad, they wanted a folding knife that was easy to conceal and carry, yet capable of inflicting massive damage with simple gross-motor-skill tactics.
There is much more at the link:
https://spyderco.com/blogs/spyderco-behind-the-grind/spyderco-civilian-reverse-s-family