Cosplay was the act of dressing up as fictional characters. According to the Fifteenth Doctor, people who did this were typically fans of the characters they dressed as. (TV: Rogue [+]Kate Herron and Briony Redman, Doctor Who series 14 (BBC One and Disney+, 2024).)
The Eleventh Doctor visited a Doctor Who convention in a parallel universe in which his life was a television series, at which his fans were impressed at what they believed to be a very convincing cosplay of himself. Despite this, he still came second in the costume contest. (COMIC: The Girl Who Loved Doctor Who)
When the Twelfth Doctor and Clara landed at San Diego Comic-Con, two cosplayers were dressed as Doc Brown and Marty McFly, while a child was cosplaying as the Star Wars character Boba Fett. (COMIC: Selfie)
Petronella Osgood was interested in cosplay. Among the items on her computer desktop was a folder for cosplay, represented with an icon of a fez. (WC: The Zygon Isolation) A tab in her Chrome window was titled 'Cosplay Costumes at C'. (WC: The Zygon Isolation)
The Chuldur were avid cosplayers, willingly killing humans so they could embody their forms and role play as them. One family in particular did this at a ball during the Regency era until Rogue and the Fifteenth Doctor stopped them. (TV: Rogue [+]Kate Herron and Briony Redman, Doctor Who series 14 (BBC One and Disney+, 2024).)
A number of individuals at the Time Hotel in 4202 could be seen engaged in cosplay for the various eras that the hotel's time portals led to. The hotel also offered a shop, Mr Benn's Any Era Clothes, designed to offer such outfits. (TV: Joy to the World [+]Steven Moffat, Doctor Who Christmas Special 2024 (BBC One and Disney+, 2024).)
Behind the scenes
Cosplay was a significant activity within Doctor Who fandom in which people dressed up as characters from the show, typically at conventions, but potentially also at Halloween, fancy dress parties, or even for no particular occasion at all.
Fans' level of participation varied, from people who bought off-the-peg, pre-made costumes, to those who paid others to manufacture bespoke costumes, to those who designed and crafted unique items from initial sketches to finished product.
Starting with DWM 522, Christel Dee gave cosplay tips for costumes of several characters, such as Ace's jacket, the Doctor's scarf and a Time Lord collar.