I want to know which was the first movie (not animated), which had only one character (which is seen) in the story. I am talking about movies like Buried and All is Lost. Not including short films or Monologue films.
I'm happy to be proven wrong, but I'm going to say Yaadein, a 1964 Indian film. From its wiki:
The film is soliloquy of a man who comes home to find that his wife and son are not at home, he assumes that they have left him and reminiscences his life with them, and scared of his life without them, he regrets his past indiscretions.
I list it because it has an entry in the Guinness Book of Records for fewest actors in a film (I believe it was the first recipient of that honour, although others have since followed).
OK, There's 3 to choose from, depending on your exact specs.
Sleep (1963) (US) Yaadein (1964) (Hindi) Portrait Of Jason (1967) (US)
Sleep (1963) - This is a 5½ hour Andy Warhol film that is just what it sounds like; one man sleeping for 5½ hours. It was shown in art houses in NYC for a limited run.
Yaadein (1964) - A Hindi film about a guy who comes home to find his wife and kids gone, and he spends the rest of the film reminiscing about family life. At the end of the film, a shadowy figure appears, so it's not truly a one-actor film.
Portrait of Jason (1967) - This is sort of like watching Big Brother (that reality show) or something; the guy drinks, smokes and babbles about his life. As the film progresses, he appears to get more and more drunk and just goes off on wild tangents.
There are plenty of others, most notably Secret Honor (1984); a well-written and acted movie centering on Richard Nixon giving a soliloquy on this life, from his Quaker upbringing to Watergate.