Hello, and welcome to my theory corner! In this episode (see others on Sonic News Network), I'll tell ya about the Zero/Light theory.
Physical and Canonical Status[]
Mostly, it's about that almost every robot Doctor Albert W. Wily is or was built by Doctor Thomas Light. Also, Proto Man has a striking resemblance to Zero, implying (depending on this theory is true or not) that maybe Blues would get an upgrade. However, that evil Doc Brow--I mean Doctor Wily stole the parts.
Quick Man Status[]
Aside from the fact that Zero is a living tank, he's also very fast. This leads me and others to the theory that it was at first, supposed to be a sort of "ProtoQuick Man". The evidence is well, Zero's quick and can face Mega Man X (character) without a sweat, being able to run circles around X, even with the Ultimate Armor on. Also, like his Non-X possible counterpart, he can ram into Mega man and deal massive amounts of damage by just touching him.
Metal Man Alt. Status[]
A counterpart to the Quick Man theory is that Zero is the X-counterpart to Metal Man.
Look at this...
...then this!
I personally believe this more than the Quick Man. However, there's one more thing to do...
Zero is another version of Mega Man (character)'s Armor[]
This Alt. Theory suggests that both Alts are right, but Light made it so Mega's two archrivals would be his powers, even them being disguised as something else. (Quick Boomerang = Zero's Sword Blasts, Metal Blade = Sword) I think this is the best answer here, but that's just me, y'know?
Well, that's all the time we have today, please tell me what you think, and leave your want-me-to-cover theories below! Goodbye!