The Magnificent Seven

Rico has been happily rewatching The Magnificent Seven (the original, not the stupid remake) and noted that several actors had changed their names:

Yul Brynner, born Yuli Bryner in Vladivostok, Russia, played Chris:

Yul sometimes claimed to be a half-Swiss, half-Japanese named Taidje Khan, born on the island of Sakhalin; in reality, he was the son of Marousia Dimitrievna (Blagovidova), the Russian daughter of a doctor, and Boris Yuliyevich Bryner, a engineer and inventor of Swiss-German and Russian descent. He was born in their home town of Vladivostok on 11 July 1920, and named Yuli after his grandfather Jules Bryner. When Yuli's father abandoned the family, his mother took him and his sister Vera to Harbin in Manchuria, where they attended a YMCA school. In 1934, Yuli's mother took her children to Paris, France. Her son was sent to the exclusive Lycée Moncelle, but his attendance was spotty. He dropped out and became a musician, playing guitar in the nightclubs among the Russian gypsies who gave him his first real sense of family. He met luminaries such as Jean Cocteau and became an apprentice at the Theatre des Mathurins, then worked as a trapeze artist with the famed Cirque d'Hiver company.

Charles Bronson, born Charles Buchinsky in western Pennsylvania, played Bernardo O'Reilly:

The archetypal screen tough guy with weatherbeaten features (one film critic described his rugged looks as "a Clark Gable who had been left out in the sun too long") Charles Bronson was born Charles Buchinsky, one of fifteen children of struggling parents in Pennsylvania. His mother, Mary (Valinsky), was born in Pennsylvania to Lithuanian parents, and his father, Walter Buchinsky, was a Lithuanian immigrant coal miner.
He completed high school and joined his father in the mines (an experience that resulted in a lifetime fear of being in enclosed spaces) and then served in World War Two. After his return from the war, Bronson used the GI Bill to study art (a passion he had for the rest of his life), then enrolled at the Pasadena Playhouse in California. One of his teachers was impressed with the young man and recommended him to director Henry Hathaway, resulting in Bronson making his film debut in You're in the Navy Now in 1951.
He appeared on screen often early in his career, though usually uncredited. However, he made an impact on audiences as the evil assistant to Vincent Price in the 3-D thriller House of Wax in 1953. His sinewy yet muscular physique got him cast in action-type roles, often without a shirt to highlight his manly frame. He received positive notices from critics for his performances in Vera Cruz in 1954, Target Zero in 1955, and Run of the Arrow in 1957. Indie director Roger Corman cast him as the lead in his well-received low-budget gangster flick Machine-Gun Kelly in 1958, then Bronson scored the lead in his own television series, Man with a Camera, in 1958. The 1960s proved to be the era in which Bronson made his reputation as a man of few words but much action.
Director John Sturges cast him as half Irish/half Mexican gunslinger Bernardo O'Reilly in the smash hit western The Magnificent Seven in 1960, and hired him again as tunnel rat Danny Velinski for the World War Two big-budget epic The Great Escape in 1963. Several more strong roles followed, then once again he was back in military uniform, alongside Lee Marvin and Ernest Borgnine in the testosterone-filled The Dirty Dozen (1967).

If you haven't seen it, click the link above and watch it now... (Hell, if you have seen it, rewatch it anyway.) All the other actors seem to have not changed their names, but are great anyway...