Hiram Percy Maxim (September 2, 1869 – February 17, 1936) was an American radio pioneer and inventor, and co-founder (with Clarence D. Tuska) of the American Radio Relay League (ARRL). Hiram Percy Maxim is credited with inventing and selling the first commercially successful firearm silencer, and also with developing mufflers for internal combustion engines.

He was the son of Sir Hiram Maxim, inventor of the Maxim Machine gun. He was the nephew of Hudson Maxim, an inventor of explosives and ballistic propellants. He had two sisters, Florence Maxim, who married George Albert Cutter, and Adelaide Maxim, who married Eldon Joubert, Ignace Paderewski's piano tuner. In 1875, the family moved from Brooklyn, New York, to Fanwood, New Jersey, with his father joining the rest of the family on weekends. At age 17, Hiram was a mechanical engineering graduate, class of 1886, of the Massachusetts Institute of Technology (then a two-year course). He went to work for various electric utility companies in Boston.

Beginning in 1892, Maxim worked at the American Projectile Company of Lynn, Massachusetts, and tinkered nights on his own internal combustion engine. He admitted his ignorance of engine developments in Germany by Maybach, Daimler, and Benz, and he later explained that he "was staggered at the amount of time required to build one small engine." Furthermore, he was appalled once he finally achieved combustion. The engine "shook and trembled and rattled and clattered, spat oil, fire, smoke, and smell, and to a person who disliked machinery naturally, and who had been brought up to the fine elegance and perfection of fine horse carriages, it was revolting."

In early 1895, Maxim visited Colonel Albert Pope in Hartford which led to his being hired for the Motor Vehicle Division of the Pope Manufacturing Company. His vehicle was not ready in time for the Times-Herald race in November, but Maxim was able to get to Chicago and serve as an umpire. He rode with the Morris and Salom entry, the Electrobat II.

In 1899, with Maxim at the controls, the Pope Columbia, a gasoline-powered automobile, won the first closed-circuit automobile race in the U.S. at Branford, Connecticut. Columbia continued to produce gasoline cars until 1913, and was also a major manufacturer of early electric automobiles and trucks.

From 1902 through 1909, Maxim was largely focused on inventing, building, marketing, and selling firearm silencers. He also developed mufflers for internal combustion engines using much the same technology.

He married Josephine Hamilton, the daughter of the former Maryland Governor William T. Hamilton December 21, 1898, in Hagerstown, Maryland. They lived in Hartford, and had a son, Hiram Hamilton Maxim, and a daughter, Percy Hamilton Maxim, who married John Glessner Lee (grandson of John J. Glessner). The John J. Glessner House designed by Henry Hobson Richardson is now a Chicago landmark.

Percy Maxim Lee (1906–2002) was president of the League of Women Voters from 1950–1958 and was appointed by President Kennedy to the Consumer Advisory Council, which she later chaired. She advocated for debates between presidential candidates and testified in the U.S. Senate against Senator Joseph McCarthy in 1955.