This character has been mentioned only and never actually shown in a comic book or on-screen. Despite their lack of physical appearances, information about them might still be relevant or interesting or at least worthy of documentation. Anything known about them is to be considered second-hand information.
Quote1 The Graysons I knew ran a circus they inherited from a clown named Anthony Zucco ... after John Grayson murdered him. Quote2
-- Owlman src

Anthony Zucco of Earth 3 was the owner of a circus that employed John Grayson. However, in order for him to "inherit" the circus from Zucco as a front for his criminal endeavors, Grayson murdered Zucco and took the circus, renaming it the "Grayson Circus".