Picture of Apollo taken from the official Planet Dob website.
Apollo is an astronaut that appears all around Dobtown(incl. Outer Circle). They are stated on the official Planet Dob website to be "a restaurant clerk in Peace 1."
When the player speaks with Apollo in Rest-N-Run, he will offer the player a Hamburger. The Hamburger can be traded to the Uronim-papa in the Park to obtain the ! echo for Piece 1.
Their name may be a reference to the Apollo space program given their astronaut suit. Coincidentally, Apollo is a deity of music according to Greek Mythology.