This is some "just shower thoughts" idea; a champion who commands/controls minions. No lore, maybe living under the fountain and finally comes out? Ulti summons a mega minion and controls it.
I actually had an idea similar to this, where it was a 'defective' minion that had achieved sentience through some magical mishap and began to evolve beyond its original purpose. He was supposed to be a sort of minion-based farm deny Champ for bot lane like Yorick and Azir were for top and mid, respectively, but the concept ended up evolving into something different entirely.
Now that the League itself is technically no longer canon in the lore, this backstory might be difficult to pull off, unless perhaps the minions are retconned into a sort of generic cannon fodder magic construct used by armies like Demacia or Noxus to help inflate the numbers of their armies, or perhaps just to safeguard certain areas of interest.
