Tails' full name was originally only going to be either "Miles Prower" or "Tails" but not both.

Yasushi Yamaguchi, who originally designed Tails for an internal competition, named him "Miles Prower" as a pun on the term "miles per hour" but the Sonic 2 development team changed his name to "Tails". As an act of rebellion, Yasushi snuck the Miles Prower name into various concept artwork and even in-game tiles. Eventually the developers reached a compromise: "Miles Prower" would be the fox's real name and "tails" would be the nickname he commonly goes by. Sonic 2 also features a cheat code that changes any in-game display of "Tails" into "Miles."