Leather

Leather was a material made by tanning animal skins. (TV: The Coach with the Dragon Tattoo)

A leather boot was found along with a single femur and an abandoned recording device containing a low-res vid-pict of a Magneton on Skaro. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

While undercover in Nazi Germany, the Seventh Doctor wore a black leather trenchcoat. (PROSE: Timewyrm: Exodus)

After the death of Lucie Miller, the Eighth Doctor added more leather to his ensemble, specifically a navy blue leather peacoat. (AUDIO: Fugitives) The War Doctor wore double-breasted trenchcoats, done in black (COMIC: The Whole Thing's Bananas) or different shades of brown. (COMIC: The Clockwise War, Ambush, The Lost Dimension; AUDIO: The Innocent; TV: The Name of the Doctor, The Night of the Doctor, The Day of the Doctor) The Ninth Doctor wore a similar style as part of his main wardrobe, a black double-breasted peacoat. (TV: Rose-The Parting of the Ways)

Some of the Doctor's companions wore leather jackets. They included Sarah Jane Smith, (TV: The Monster of Peladon) Rose Tyler, (TV: The Stolen Earth / Journey's End) Martha Jones, (TV: The Shakespeare Code) Ace, (TV: Dragonfire) Amy Pond, (TV: Victory of the Daleks) Clara Oswald (TV: The Magician's Apprentice / The Witch's Familiar) and Yasmin Khan. (TV: It Takes You Away)

The Master wore leather gloves during his sixth (TV: Terror of the Autons-Frontier in Space) and war incarnations. (AUDIO: Killing Time) He also wore a black leather duster coat when possessing Bruce, (TV: Doctor Who), and also a double-breasted trenchcoat of black leather as part of his Nazi costume when during his spy incarnation. (TV: Spyfall)

Davros wore a black leather tunic. (TV: Genesis of the Daleks, Destiny of the Daleks, Resurrection of the Daleks, Revelation of the Daleks, The Stolen Earth|Journey's End, The Magician's Apprentice|The Witch's Familiar; COMIC:  Emperor of the Daleks; AUDIO: I, Davros, Davros, The Juggernauts, The Dalek Defence, The Triumph of Davros)

Cinder wore an asymmetrical, double-breasted jacket of black leather. (COMIC: The Bidding War, Relative Dimensions)

Candy DuFries always carried a battered leather satchel full of watercolours. (PROSE: Eternity Weeps)

The symbiotic Fliis, as part of their plan to take over humans on Earth in the 20th century, disguised themselves as leather jackets to trick people into wearing and bonding with them. (COMIC: Fashion Victims)

In October 2016, Ram Singh suggested that a male skin-peeling dragon make Coach Dawson's skin into leather, "make a chair or something", in order to preserve his mate. (TV: The Coach with the Dragon Tattoo)

In the 24th century, hidehogs were genetically engineered animals used to produce leather. (PROSE: To the Slaughter)

The skins of ghouties could be made into leather. They looked like a cross between a donkey and a three-toed sloth and were found on Thanaxos. (PROSE: The Mary-Sue Extrusion)

The Slabs were made of leather. (TV: Smith and Jones)