Actually AdBlock Plus was a fork of AdBlock, by a different person, because AdBlock was no longer maintained.
I suspect AdBlock(er) Ultimate is yet another unrelated extension from completely different people.
It's a similar story with uBlock. I think the uBlock dev wanted to stop, handed off dev to someone else who fucked up. So it was forked into uBlock origin.
tl;dr they're all adblocking software from different people, who don't work together.
* AdBlock
* AdBlock Plus
* AdBlock Ultimate, now AdBlocker Ultimate
uBlock has:
* uBlock
* uBlock Origin
...and I can never tell the difference.