Penelope Platypus is a character that appears in the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics. She is a mobian platypus and a member of the Substitute Freedom Fighters who hails from Downunda. Penelope was one of several Freedom Fighter recruits chosen by Sally Acorn for a special mission meant to determine their potential. The mission resulted in the uncovering of Dr. Ivo Robotnik's Auto Automatons, a scheme that the Substitute Freedom Fighters, aided by Geoffrey St. John, were able to thwart.
Penelope and the others would later come to the aid of Sally and her more experienced squad on several occasions, including stopping an amnesia-ridden Sonic from defeating the Knothole Freedom Fighters, a bizarre conflict involving a video-game link between Mobius and Earth, and a period of time in which Sonic was bereft of his speed and had to rescue the Knothole Freedom Fighters from captivity.
Two years later, Penelope would later be elected to serve on the Council of Acorn. She and her associates agreed not to launch a preemptive mission to Angel Island in the face of the threat presented by Enerjak, feeling that they had too little information on him. She also denied the Freedom Fighters' request to authorize a mission to retake Freedom HQ from the Suppression Squad, and with the rest of the council presided over a disciplinary hearing for Sally after she disobeyed those orders. Like all members of the council but her former teammate Hamlin, however, she voted to drop the charges against Sally.
- Penelope is known to have a counterpart from Anti-Mobius who was briefly involved with Evil Sonic, but unlike Buns Rabbot she did not join the Anti-Freedom Fighters in search of vengeance.
- Penelope, along with Hamlin, holds the sixth longest "non-appearance gap" in the series (StH: #38-#180).
- In Issue #197, Penelope is colored violet instead of dark blue.