This is one of Thomas' most popular costumes: Spaceman Spiff, from Bill Watterson's comic strip Calvin and Hobbes.
When he presented this at a Philcon masquerade, Thomas used special goggles tht incorporated eye-shapes pre-drawn on Post-It notes. Every few seconds, he ripped off the top set to expose a new set of eyes: round, square, triangular, etc -- just the way Spaceman Spiff's eyes change in the comic strip.
Invariably, when Thomas wore Spaceman Spiff, someone would say, "Where's Hobbes?" This drove Thomas spare. You see, Hobbes never appeared in any of the "Spaceman Spiff" adventures. "Spaceman Spiff" was a game that Calvin played alone, without Hobbes.