What is the name of Sonic's primary antagonist?

Sonic’s primary antagonist is Dr. Eggman, also known as Dr. Ivo Robotnik. He is the recurring mad scientist who schemes against Sonic and repeatedly attempts to conquer the world.

Eggman was created by Sega designer Naoto Ohshima and debuted as the main villain of the original Sonic the Hedgehog. His plans commonly involve capturing animals, building armies of robots, controlling the Chaos Emeralds, or constructing enormous weapons and cities under his command. Although he is usually Sonic’s enemy, some stories temporarily force the pair to cooperate against a greater threat.

The name can cause confusion because “Dr. Robotnik” and “Dr. Eggman” refer to the same character. “Robotnik” was widely used in early Western releases and some English-language adaptations, while “Eggman” was the original Japanese name and became the standard name across the games. Dr. Neo Cortex belongs to Crash Bandicoot, and Dr. Wily is a recurring Mega Man villain, so neither is part of Sonic’s central rivalry.