Now it's riding into American theaters again, longer - a full three hours - and more ornery than ever.
MGM has assembled the first complete edition of the movie's English-language version, restoring trimmed-out sequences and bringing stars Clint Eastwood and Eli Wallach back to the studio for new dubbing sessions. The result is as eye-opening and nerve-jangling as fans of the shorter cut could wish.
The film originally opened at a time when "spaghetti Western" was also a familiar phrase, referring to Italian productions that had a sharply different look from the scenic John Ford epics and psychologically fraught "adult Westerns" that had hitherto defined the genre.
The new breed came of age when Mr. Leone's earlier hits - "A Fistful of Dollars" and "For a Few Dollars More" - took US audiences by storm, making Mr. Eastwood a wide-screen superstar in the process.
"The Good, the Bad and the Ugly" took matters to their next logical step.
Its story was in Leone's patented vein, throwing three tough hombres - a bounty hunter, a Mexican bandit, and a "good guy" as ferocious as both of them - into a series of rivalries and partnerships against a tumultuous Civil War backdrop. Its style was also pure Leone, contrasting extreme close-ups and telescopic long-distance shots in patterns of great rhythmic force.
If the movie looks less revolutionary today than when it was new, it's partly because so many Hollywood directors - led by Sam Peckinpah, who wasn't nicknamed Bloody Sam for nothing - eagerly imbibed its lessons. Leone also did himself one better in "Once Upon a Time in the West" two years later. It remains a powerful spectacle, though, and a vivid time capsule of a bygone Western era.
Not to mention that legendary Ennio Morricone score - Doodle-doodle-doo, wah wah wah.... Some of us are still humming it 36 years later.
• Rated R; contains violence.