Sonic CD/Characters

Sonic CD has a limited cast of characters, though for its time it was fairly large. The characters are as follows:

Sonic
Sonic is the star, as usual. Like Sonic 1, he is the only playable character. Sonic sets out for the Little Planet to stop Eggman, and runs into Amy Rose, who gets captured.

Amy
Amy is a young hedgehog who is a big fan of Sonic. In the first level, Palmtree Panic, Amy will latch on to Sonic when she gets close. A little later, Metal Sonic bursts through a wall of spikes and kidnaps her. This is her first appearance in a Sonic game.

Metal Sonic
Metal Sonic is Eggman's counter to Sonic. This isn't the first robotic Sonic Eggman has built, but it's by far the longest lasting design. After kidnapping Amy, Metal Sonic races against Sonic later on. Metal Sonic first appears in this game, and recurs in several games after this, even as a playable character.

Eggman
Eggman is Sonic's eternal nemesis. In this game, Eggman's goal is to steal the Time Stones from the Little Planet to conquer the world. He kidnaps Amy to lure Sonic to him, which turns out to be his downfall.