I do have many, but I'll start with the oldest and go to my newest
Talonflame
The first pokemon I ever got was a fletching on my DS back when pokemon Ultra moon first released, I don't think it ever got a name but that talonflame lived with me for over 3 years, assisting me and carrying me through battle
Noivern
This was in the same game cartridge, same everything. My first encounter in one of the routes through the first in Ultra moon was a female noibat I named Luna. Ever since, in any game I've played I get a female noibat and grow with it, naming it noibat each time.
Noivern is seriously a great pokemon
Espeon
A pokemon that seems to appear to me every game I play as my first eeveelution, and helping me beat Scarlet & Violet, my Espeon named Xikphryan who has never left my party.
Ampharos
My first ever shiny from Violet, one of my favourites. They may not appear much but I stumbled upon this shiny and every time I used it in battle it won.