The Sigma Circular, also known more simply as Sigma, is a sentient machine created by Gold Drive and Roidmude 004 to dominate all of humanity, serving as the final antagonist of Kamen Rider Drive.
History
During the first attempt to activate this machine, Medic was originally meant to be a sacrificial vessel, but Brain takes her place to save her from being killed.
After escaping, Gold Drive and the Reaper Legion infiltrated the Special Defense Center headquarters, and placed Sigma under evolution process before Drive, Mach, Chaser, Heart and Medic could stop his plan to create a second Global Freeze.
Sigma's evolution was completed, activating the second Global Freeze just before Drive and Heart arrived to stop the machine. Sigma was destroyed by the combined force of Drive Type Tridoron's Rider Kick and Heart Super Evolved's strength punch. With its destruction, the Global Freeze ended and all the humans who were transformed into data were returned to normal.