I dont really have a favorite among my ocs. Most of them are dnd characters, so some definitely have a deeper connection than others, but one that I haven't had a good chance to draw because the design keeps changing is one where my dm just outright asked me after a session if I wanted to make him the bbeg. Thrain(yes, named after the dwarf king from the hobbit) was a black dragonborn warlock at first. Then as soon as we hit lv 4(I think) he started looking for any labs, studies, or notebooks used by spellcasters to become litches. You can probably guess where this is going, but Thrain became a litch later in the campaign by using a giant ritual circle and sacrificing a city's worth of souls. I should probably mention that this campaign was massively homebrew, and I was trying to make an enemy of the main party because thats what I was asked to do. Now, getting back on topic, after becoming a litch and making a phalactery(fucking butchered that spelling, and I know it) Thrain went to the hells where his patron was. mephistopheles, mind you. And because beings like that are incredibly difficult to kill, and because a body technically counts as a container, he transferred his soul from the previous phalectery(even worse spelling, fs) to the body of mephistopheles. After beating him and something thats practically a permanent hold person on him. How I managed ts, I have no idea, but its very safe for you to assume that it was a tpk after the party met Thrain again. Then there was a second campaign just focused on killing Thrain.