What is the name of the chameleon ninja character in Sonic?

The chameleon ninja character in Sonic is Espio the Chameleon.

Espio is a purple chameleon and a member of the Chaotix detective team, alongside Vector the Crocodile and Charmy Bee. His ninja training gives him a quieter, more disciplined personality than many other Sonic characters. He can use ninjutsu techniques and camouflage himself, making stealth his defining ability.

Espio debuted in Knuckles' Chaotix for the Sega 32X in 1995. He later became playable in Sonic Heroes, where Team Chaotix worked as a detective agency and Espio filled the team's speed role. Vector provided power, while Charmy handled flight. Espio's invisibility and martial-arts skills also appear in several later Sonic games and spin-offs.

A common mix-up is confusing Espio with his Chaotix teammates. Vector is the crocodile detective, Charmy is the flying bee, and Mighty is an armadillo who is associated with the wider Sonic cast but is not the chameleon ninja.