James Montgomery Doohan (/ˈduːən/; March 3, 1920 – July 20, 2005) was a Canadian actor, best known for his role as Montgomery "Scotty" Scott in the television and film series Star Trek. Doohan's characterization of the Scottish chief engineer of the Starship Enterprise has become one of the most recognizable elements in the Star Trek franchise, and inspired many fans to pursue careers in engineering and other technical fields. He also made contributions behind the scenes, such as the initial development of the Klingon and Vulcan languages.

Prior to his acting career, Doohan served in the 14th Field Artillery Regiment of the 3rd Canadian Infantry Division. He also served as an Artillery Forward Observation Officer (FOO) and pilot. He saw combat in Europe during World War II, including the D-Day invasion of Normandy, in which he was wounded, apparently by friendly fire. After the war, he had extensive experience performing in radio and television, which led to his role as Scotty. Following the cancellation of the original Star Trek series, Doohan was typecast and had limited success in finding other roles; he returned to play the character in the animated and film continuations of the series, and made frequent appearances at Star Trek conventions.

Doohan was born in Vancouver, British Columbia, the youngest of four children of William Patrick Doohan and Sarah Frances (née Montgomery), who both emigrated from Bangor, County Down, Northern Ireland. His father, William Doohan, was born in Belfast, and was a pharmacist, veterinarian and dentist, and a member of the Pharmaceutical Society of Ireland. William Doohan owned a chemist shop in Main Street in Bangor beside Trinity Presbyterian Church and reportedly invented an early form of high-octane gasoline in 1923. Doohan's 1996 autobiography recounted his father's serious alcoholism.

The family moved from Vancouver to Sarnia, Ontario. Doohan attended high school at Sarnia Collegiate Institute and Technical School, where he excelled in mathematics and science. He enrolled in the 102nd Royal Canadian Army Cadet Corps in 1938.

In 1939, Doohan enlisted in the Canadian Army, joining the Royal Canadian Artillery, 14th (Midland) Field Battery of the 2nd Canadian Division. From there, he was moved to the 13th Field Regiment of the 3rd Canadian Division in their 22nd Field Battery. By 1940 he was a lieutenant and was sent to train in Britain. He first saw combat on D-Day, landing in the second wave in a reconnaissance party at Juno Beach. The 13th Field Regiment was interspersed with the Regina Rifle Regiment landing at Nan Sector of Juno Beach. After shooting two snipers, Doohan led his men to higher ground through a field of anti-tank mines, where they took defensive positions for the night. Crossing between command posts at 23:30 that night, Doohan was hit by six rounds fired from a Bren gun by a nervous Canadian sentry: four in his leg, one in the chest, and one through his right middle finger. The bullet to his chest was stopped by a silver cigarette case given to him by his brother. His right middle finger had to be amputated, something he would conceal on-screen during most of his career as an actor, sometimes with a flesh-colored glove with a faux finger.

Doohan graduated from Air Observation Pilot Course 40 with eleven other Canadian artillery officers and flew Taylorcraft Auster Mark V aircraft for 666 (AOP) Squadron, RCAF as a Royal Canadian Artillery officer in support of 1st Army Group Royal Canadian Artillery. All three Canadian (AOP) RCAF squadrons were crewed by artillery officer-pilots and accompanied by non-commissioned RCA and RCAF personnel serving as observers. Although he was never actually a member of the Royal Canadian Air Force, Doohan was once labelled the "craziest pilot in the Canadian Air Force". In the late spring of 1945, on Salisbury Plain north of RAF Andover, he slalomed a plane between telegraph poles "to prove it could be done", earning himself a serious reprimand. (Various accounts cite the plane as a Hurricane or a jet trainer; however, it was an Auster Mark IV.)

After the war, Doohan moved to London, Ontario, for further technical education. After hearing a radio drama and believing he could do better, he recorded his voice at the local radio station, and learned about the Lorne Greene Academy of Radio Arts in Toronto. There he won a two-year scholarship to the Neighborhood Playhouse in New York City, where his classmates included Leslie Nielsen, Tony Randall, and Richard Boone.

In 1946, he had several roles for CBC radio, starting January 12. For several years, he shuttled between Toronto and New York as work demanded. He made his TV debut as a detective on the show Martin Kane, Private Eye, and appeared in 54 episodes. He estimated he performed in over 4,000 radio programs and 450 television programs during this period, and earned a reputation for versatility.