Matt Helm is a fictional character created by American author Donald Hamilton (1916–2006). Helm is a U.S. government counter-agent, a man whose primary job is to kill or nullify enemy agents—not a spy or secret agent in the ordinary sense of the term as used in most spy thrillers.

Helm appeared in 27 adventure/suspense novels by Hamilton, first published in 1960, and the character was later adapted into film, television and other media. The 1960s film series, starring Dean Martin, featured a campy, humorous tone quite different from the gritty novels. The 1970s television series featured a more serious dramatic tone but was a relatively standard private investigator series with little connection to Hamilton's books.

Published between 1960 and 1993, the 27 books in the series portrayed Helm, who acquired the code name "Eric" during his secret wartime assignments, as jaded, ruthless, pragmatic, and competent. The series was noted for its between-books continuity, which was somewhat rare for the genre at the time. In the later books, Helm's origins as a man of action in World War II disappeared and he became an apparently ageless character, a common fate of long-running fictional heroes.

The first book in the series, Death of a Citizen, takes place in the summer of 1958, 13 years after the end of the war. In the book, other characters describe Helm as verging on middle age and apparently soft and out of shape, although no specific age for him is given. In the next story, which apparently takes place in the summer of 1959, a hostile agent from a rival American spy organization taunts Helm as a shopworn 36-year-old and clearly over the hill as a physical specimen. Later in the book, Helm himself says that he is 36 years old. Writer Hayford Peirce examined the issue of Helm's age, and found this figure to be improbably young given the information about Helm's background in Death of a Citizen. Peirce postulated that Helm was actually several years older than the 36 years mentioned in The Wrecking Crew and that he was probably born around 1918. By The Betrayers, the tenth book, the age issue vanishes completely.

Critic Anthony Boucher wrote: "Donald Hamilton has brought to the spy novel the authentic hard realism of Dashiell Hammett; and his stories are as compelling, and probably as close to the sordid truth of espionage, as any now being told." Golden Age mystery writer John Dickson Carr, who began reviewing books for Ellery Queen's Mystery Magazine in 1969, "found Donald Hamilton's Matt Helm to be 'my favorite secret agent,'" wrote Carr's biographer, noting that Hamilton's books had little in common with Carr's. "The explanation may lie in Carr's comment that in espionage novels he preferred Matt Helm's 'cloud-cuckooland'. Carr never valued realism in fiction."

(all by Donald Hamilton)

All of Hamilton's Matt Helm novels were first published in the United States by Fawcett Publications under their Gold Medal imprint.

These titles have since been republished by Titan Books.