There’s self, there’s other and there’s other-other. Most of of us believe we know what the first two are. The third may sound a little weird, especially since we each have several of them.
Fancy names like sub- and multiple personalities, semi-autonomous fragments, dissociated aspects, even PTS, etc. have been given to what are actually normal adaptive behaviors. To survive, we do need to rearrange our inner beings frequently and choose which components to reveal in differing circumstances.