|This character exists primarily or exclusively within the Sonic Underground continuity.|
Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
Thelonious was a monk who was put in charge of the second stage of the Sonic Underground's training. He is an anthropomorphic dog in orange robes.
He trained them to work together and use their Medallions. He didn't feel the triplets were ready when they left him, but allowed them to go nonetheless.
- Thelonious' name is a reference to jazz pianist Thelonious Monk.