Zipper is a yellow rabbit with a white muzzle, buck teeth, blue overalls, and a turquoise sun visor. His eyes are green and he has purple eyelids and three eyelashes on each eye. He has a brown nose and small eyebrows. There is a zipper on the back of Zipper's overalls, which may be the source of Zipper's name. It is easily visible when seen from behind, which causes Zipper to turn around and comment saying not to look at the zipper, as it "spoils the magic". It's a running joke that villagers think he is someone in a costume though he has defended his appearance saying it is, in fact, not a costume. In Pocket Camp, he seems sensitive about it, claiming it's rude to call it (his appearance) a costume and that this is just how he looks.
In City Folk and New Leaf
After being approached, Zipper starts dancing and his theme begins to play. As the player leaves the Town Plaza, the music fades and Zipper sighs heavily. When talked to, Zipper will ask the player to search for bunny eggs that are buried around the town. Opening these will reveal a "surprise". If the player repeatedly talks to Zipper without finding any bunny eggs, he will say to look for bunny foils instead, which are also called prize tickets. Zipper will give the player Furniture from the Egg Series or his picture each time the player finds one bunny foil or grand prize ticket inside an egg and gives it to Zipper.
During the event, villagers will usually speak of Zipper in a derogatory manner. Normal villagers appear to be scared of Zipper or worried about his health. It appears that Zipper is unhappy with the choice of uniform and job, by mentioning that he wants a new job under his breath, and will occasionally mention how uncomfortable it is under the suit.
After the Welcome amiibo update for New Leaf, when visiting Zipper's RV, the description will say, "Camping gives Zipper a chance to finally get out of that stuffy old costume and- er, we're being told in no uncertain terms that it is NOT a costume."
In New Horizons
In New Horizons, Zipper arrives on the island on the first day of the Bunny Day event to tell the player about the festivities and present the Bunny Day bed DIY recipe, but asks that the player keep his visit a secret. He will remain on the island for the entire day. Zipper returns on the final day of the event and can be found in the Resident Services plaza, where he will offer additional crafting recipes and exchange eggs. Zipper remains guarded about the zipper on his back, and villagers will mention teasing him. If the player attempts to talk to Zipper while standing behind him, Zipper will become irritated, and will demand the player stops. This has no effect on Zipper's attitude or actions in general.
Zipper shares his birthday with Hopkins, who is also a bunny. They both have a birthday on March 11th.
Throughout the series, Zipper has staunchly expressed that he is, in fact, not wearing a costume, though there is an obvious zipper on his back. He even alludes to this in New Leaf: When players talk to him from an angle that makes him turn to reveal the zipper, he says not to stare at it, as it'll "ruin the magic".
Warning: Theory starts here.
Fans have come up with many theories as to Zipper's true identity, though many of them are easily debunked:
Phyllis: People theorize that Zipper is Phyllis in a costume due to their similar habit of making asides in grayed-out text, about how much they dislike their jobs. This has been debunked in all games prior to New Horizons, as Phyllis is still present at her job in Town Hall or the Post Office, or in The Roost, whenever Zipper is present in the player's town. Theorists have responded by purporting that Pelly could be taking over her role as Zipper when she is busy, as they have different shifts.
Tortimer: People also theorize that Tortimer is Zipper, but he too is present at the Town Hall or in Island Tours (in New Leaf) when Zipper is present on Bunny Day.