"inventant un double...
"People do it everyday, they talk to themselves... they see themselves as they'd like to be..." - from Fight Club
This is a list with films where a character imagines and interacts with another persona - simulacra or real entities reflecting someone living, someone dead, a conscious/unconscious fantasy or a "delusion" resulting from a dissociative identity disorder, schizophrenia, psychosis and so on. It's a wide-reaching topic and as personal list I don't know how to describe it. It's about the creation of an image of someone else, summoning others. These films are about doubles, alter egos, the mind and how it can create from impressions and so on. I also included films where characters create whole worlds of imagination with different personas (based on their memory and dreams for example), where different selves are found due to time travel or parallel universes, characters create AI, new species, clones or androids, there appear tormenting spirits based on fear, with people simply fantasizing about a different hopeful future-ideal self or evoking a personal god and so on. Note not all films listed have to relate to the opening quotes.
It is likely that a common characteristic of these films is the high abundance of mirrors in these films - for they are symbols (of for example reflections, replications, simulations, doubles, many-worlds, narcissism, confusion), portals to other realms, aesthetically pleasing (and difficult to work with) objects and stimulus to characters (self-observation, gaining insight) and so on.
In no particular order.