The idea of making just one actor or actress the lynchpin of a feature-length movie is enough to turn most filmmakers pants-on-head levels of crazy. It's one thing to make a successful film with an entire ensemble at your fingertips, but it's quite another to create something magnificent - or even watchable - with one lone performer.
These "one-man shows" are a painful viewing experience when they don't work out, especially once the initial gimmickry falls away to reveal an underwhelming story or a mediocre performance.
Because these types of movies succeed or fail based entirely on those two things: Story and performance. It's crucial that both of those elements knock it out of the park, because there are no other distractions for the audience to get swept away by. And once the viewers are lost, there's really nothing left to reel them back in.
On the other hand, when it works, this strange sub-genre of dramatic film can be a truly, uniquely satisfying experience. Sometimes it's even enough to redefine an actor's career.
Now in the interest of transparency, some of the films on this list do technically have more than one actor on the roster - occasional cameos or supporting voice actors, that sort of thing - but for the most part, it's all on the shoulders of just one man or woman.