What bottom bracket is this and why does it have a lockring?
It's probably a cup and cone bottom bracket with the splined tool interface rather than wrench flats or pin holes. Most recent ones are like this, I believe as a function of what tools now make up the standard arsenal at bike factories. Or it may be a cartridge BB with a lockring, which have existed but aren't common. In either case, you remove it by loosening the lockring and then removing the cups.