This photo shows the input shaft of an air compressor head.
The splined cog-looking disc around the shaft is actually a sort of threaded nut which screws into the larger disc around it. It serves to hold in the bearing on this side.
It may be that this part requires a unique, specialized tool - but I suspect there may be something that is "standard" but perhaps uncommon instead. In many environments a compressor head doesn't require such frequent maintenance that a totally unique tool would be inconvenient.
Note the bolt heads around the splined part don't allow for very much clearance - about 3/16" or ~5mm.
I think given some brute force it probably could be unscrewed using a punch or even a screwdriver used as a punch, but I don't want to damage it.
Possibly an adjustable pin spanner might fit - but the only ones I have are pretty lightweight. Also I think the pins would probably pop out of the grooves (they are usually used in holes instead).
This compressor head is vintage, I think about 70 years old.