Thelonious is the (former) secondary antagonist-turned-one of the supporting protagonists from Shrek and Shrek 4-D.
He is also a minor character in Shrek in the Swamp Karaoke Dance Party.
He later appears in the climax during the I'm a Believer song.
Shrek in the Swamp Karaoke Dance Party
He reappeared in Shrek in the Swamp Karaoke Dance Party, as he sings with The Gingerbread Man.