A tricorn was a type of hat.
Worn by the Doctor
The Second Doctor once wore a British Army tricorn as a disguise. (TV: The Highlanders [+]Loading...["The Highlanders (TV story)"])
One of the Doctor's incarnations predating the First Doctor wore a tricorn. (TV: The Brain of Morbius [+]Loading...["The Brain of Morbius (TV story)"]) The Eighth Doctor later found his old tricorn in the TARDIS secondary control room, reminiscing that it had been "ages" since he'd worn it. (TV: The Dying Days [+]Loading...["The Dying Days (novel)"])
The Second Doctor had a tricorn hat in his TARDIS wardrobe. (PROSE: Twilight of the Gods [+]Loading...["Twilight of the Gods (NA novel)"])
Companions
Amy Pond wore a black tricorn when using a cutlass to save the Eleventh Doctor and Rory from the pirates of the Fancy. (TV: The Curse of the Black Spot [+]Loading...["The Curse of the Black Spot (TV story)"])
Worn by Others
Henry Avery, a leading pirate, wore a black tricorn. (TV: The Curse of the Black Spot [+]Loading...["The Curse of the Black Spot (TV story)"], A Good Man Goes to War [+]Loading...["A Good Man Goes to War (TV story)"])
Avatar wore a tricorn hat. (PROSE: Of the City of the Saved... [+]Loading...["Of the City of the Saved... (novel)"])