This was made clear by the European auteur directors often working with the same talent on multiple films (something also replicated around the world in cinema). One of the more famous of these director/actor relationships was that of actress Anna Karina and director Jean-Luc Godard, who were also married for four years.

The British Film Institute recently posted a quick video showing off the many faces and personalities of Karina, without whom many of Godard's greatest works would not have been the same:

An interesting detail about Karina is that she was Danish, so she didn't speak French very well when she first started acting in France. Eventually though, her and Godard would become linked forever, making a total of eight films together, most notably Vivre Sa VieA Woman Is a Woman, Band of Outsiders, and Pierrot le Fou.

Here's an interview from the Criterion Collection on how she met Godard:

And a much older interview with her (she really isn't taken as seriously as she should be):

What's your favorite collaboration between the two of them?

Source: BFI