On the encyclopedia on this site under Amy Rose, it says that Zero is an E-100 robot. (Like Gamma) Is he? He looks nothing like Gamma? And when Dr. Eggman asks his E-100 robots to bring Froggy back, Only Gamma brings the right frog and the others are sent out of the Egg Carrier. THen why do you fight E-105 Zeta in the egg carrier and why dose he look upgraded? Thanks!
1) Zero is the prototype for the E-100 series. Zero is E-100 Alpha. Then there's E-101 Beta, E-102 Gamma, etc (following the Greek alphabet).
2) Ticked off at the other robots for not finding Froggy, Eggman gives Gamma some actual missions, and leaves the other E-bots to protect the areas that'd most likely be trouble. Zeta was upgraded to protect Hot Shelter.

--True Red & SA Tails