E-117 Sigma was an E-100 Series robot.
Sigma was the eighteenth E-Series robot created by Dr. Eggman. At some point E-102 Gamma tracked it to Old Megaopolis in Northamer. During the battle Gamma was infected with Zero Viruses, causing him to receive multiple liberation confirmations, but it continued its pursuit of Sigma regardless and destroyed it, freeing its Mobini. (ASUB)