You hear lots of stories about how famous films later get made into knock-off "Made for TV" movies, but in this case, 12 Angry Men started out as a play written for television by a guy named Reginald Rose. It was only after this play became a success that Rose was approached by actor Henry Fonda (who plays Juror #8) to make a feature film out of the script. Neither Rose nor Fonda had ever produced a movie before, but they both figured, "Hey, how hard could it be?" and went on to make movie history.
Despite the movie's fame today, making the thing wasn't easy for either Fonda or Rose. Since they were both first-time producers, they took a gamble on a first-time feature film director, Sidney Lumet. They spent only a few hundred thousand dollars filming the thing, which makes sense, given that the whole movie is just twelve actors in one room. There aren't many giant explosions or car chases.
And by "there aren't many," we mean "there aren't any."
By the time all was said and done, 12 Angry Men flopped at the box office, and Henry Fonda vowed never to produce a movie again. It was only later that the movie got traction with viewers on TV and became an American classic. By that time, Fonda and Rose were on to different stuff.