For me there’s two separate participants, a ‘talker’ and a ‘listener’. My mind identifies more with the talker, because that’s the one that has agency. Since there are two participants, both of which are me, I talk in 1st person plural (‘we’ve got to do …’, 'we thought about this earlier’). I stopped being afraid of being alone after I started having an internal dialogue around the age of 11, since having a second participant in the conversation meant I was always in company.
Edit: Wow, looks like there’s a lot more diversity in this than I was expecting
My internal monologue is usually just like a commentary of my own voice, or at random times I just talk it out loud cause I find it nice to just speak, but I can mimic others people voices in my internal monologue if I felt like it; sometimes, my mind never talks at all and uses visual to think which what I do most of the time, it’s quite peaceful to have a break from the noise.