My headcanon is that Mr Makuro is Takanuva as a Turaga. If you look closely, you’ll notice that Mr Makuro has original Bionicle feet instead of any type of Hero Factory foot. He also wears a Turaga-like robe.
I theorise that after the Battle of Spherus Magna, most of the Toa were too battle scathed and unfit to fight anymore, and therefore retired and eventually became Turaga.
New threats arose, but no-one was there to stop them. So Takanuva created the Hero Factory - a place where new Heroes could be made to counter the evil forces. Once they became old, new Heroes could simply take their place.
Around the towering factory, a city was born, a sanctuary for Matoran and Turaga alike. Hydraxon eventually joined the Heroes, and became known as Von Ness. After the infamous ‘Von Ness Mission’ Von Ness crash landed in a scrapyard and rebuilt his body using pieces of deceased Nuhvok. He obtained the Black Hole Staff from the junkheap, declaring himself Von Nebula.
Still, that’s just 8 year old me’s silly headcanon.