The Maxim was the first true self-powered machine gun*, a recoil-operated fully-automatic belt fed weapon produced by Sir Hiram Stevens Maxim, an American-born inventor who moved to England at the age of 41.
Maxim's attention was drawn to guns in 1881, when a friend famously advised him "If you want to make a pile of money, invent something that will enable those fool Europeans to cut each other's throats with greater facility." He produced his first gun in 1885, an extremely bulky device with a distinctive bulge at the rear for a rotary crank to reverse the movement of the block, and a unique pointer-operated fire regulator which allowed the weapon to fire at any speed from 1 RPM to 600. Both were eliminated in later designs for simplicity, the crank assembly being replaced with a toggle joint that was the forerunner of that used on the Borchardt C-93 and Luger P08.
Despite some scepticism from early buyers (the Tsar of Russia's officers, when the 1885's mechanism was explained to them, laughed and stated nobody could operate the crank 600 times a minute, while the King of Denmark, on being told how much each round cost, told Maxim one of his guns would bankrupt Denmark in half a day) the gun was an instant success, and was adopted by many national militaries in a variety of variants and calibres. It saw combat from British use in The Gambia in 1888 to the end of the Second World War, eventually being supplanted by lighter and more efficient designs. Larger versions of the Maxim were also used as anti-aircraft guns, with the most well-known examples being the British "pom-pom" guns.
Maxim's gun company was established with the help of the Vickers steel company of Great Britain and ultimately absorbed into it, joining with rival Nordenfeldt of Sweden in between; Albert Vickers would later produce his own redesigns of the Maxim, the Maxim-Vickers and later the Vickers Gun.
(*While a Swedish Army Lieutenant, D.H. Friberg, had patented a design for a recoil-operated firearm action using locking lugs similar to those used by many later automatic weapons (such as the Russian DP-28) in 1870, with early drawings for a weapon based on it dating back to 1882, Friberg's design was impractical due to rapid residue buildup from use of black powder, and it is unclear if any firing weapon was produced before Maxim's gun in 1885. Rudolf Henrik Kjellman latter refined Friberg's design to use Swiss 6.5x55mm smokeless powder cartridges in 1907, adding a bipod, water jacket and forward grip and replacing Friberg's hopper feed with a detachable box magazine: this, the "Kjellman Light Machine Gun," was a commercial failure with only ten examples produced.)