One of the best men's adventure paperback series of the 1970s began with THE TARGET IS H, which reveals the origin of the Penetrator. Most (all?) of the Penetrator books were written, separately, by Mark Roberts (the odd-numbered entries) and Chet Cunningham (the evens), and were published by Pinnacle, which had found gold with its influential Executioner series by Don Pendleton.
I prefer the Penetrator series to the Executioner because of its varied plots and slight SF angle that occasionally push it closer to spy fiction than crime drama. THE TARGET IS H, however, features a purely Pendletonian plot, as hero Mark Hardin targets the Los Angeles heroin trade led by Don Pietro Scarelli, who works for a mysterious British mobster known as Sir Lordship.
Hardin's first mission is motivated by revenge, as we learn through flashbacks how he came to be gunning for mobsters. He was an expert tracker and sharpshooter in Vietnam who nearly died while investigating the appearance of American medical supplies and weapons on the black market. The U.S. Army personnel involved with the crimes attacked and beat Hardin nearly to death. After his long recovery, Hardin received his honorary discharge, and came to Los Angeles, where the orphan had been reared in a number of foster homes before attending UCLA on a football scholarship.
Hardin, nicknamed the Penetrator in 'Nam, met a retired college professor, William Haskins, who invited the lonely nomad to live in his hidden desert bunker, a luxurious stronghold buried deep within an abandoned mine. There, Hardin trained his mind and his physical body, thanks to heavy mentoring by Haskins and an elderly Cheyenne Indian named David Red Eagle. He also fell in love with the professor's niece, Donna Morgan, who was shortly thereafter killed when the car she and Hardin were riding in was forced off the side of a mountain by mobsters, who, at that moment, forever earned the wrath of the Penetrator.
Just 156 pages long, THE TARGET IS H is a little choppy, as it doesn't really have enough room to tell Hardin's origin and settle into its adventure plot against the drug cartel. It is rapidly paced, of course, but one wonders why the origin story didn't receive the entire book. It's a good read, but the Penetrator series would get even better.