>>715853539
it's literally confirmed as Knuckles by the guy who animated the eyes, colored them and put them in at the behest of Sega. Sonic 3 was coming out during production and they wanted Knuckles teased.
so Ron Myrick did it.

makes sense its just the eyes, because that's all the public was allowed to see until the game released. he's just some eyes in a bush on the cover art.