Marco Polo

Marco Polo, born in 1252 (TV: Marco Polo) and living until the early 14th century, (PROSE: A History of Humankind) was a Venetian trader and explorer whom the First Doctor and his companions travelled with across Asia. (TV: Marco Polo)

Although he was not the first European to visit China, he was the first to write a detailed account of his experiences there, publishing it under the title The Travels of Marco Polo circa 1300. (PROSE: A History of Humankind)

Biography
Polo, with his father and uncle, left for Cathay in the year 1271. By his twenty-fifth birthday in 1277, he had come into the service of Kublai Khan. In 1287, Marco, his father and uncle asked the Khan to be permitted to return home. The Khan refused.

Polo encountered the First Doctor, Susan, Ian and Barbara on the Plain of Pamir in 1289 and promptly seized the TARDIS as a gift for the Khan. He hoped it would be sufficiently impressive to buy his way out of the Khan's service so he could return home. The Doctor and his companions were forced to make a long overland journey with Polo, during which time they got to know him well. He helped prevent an assassination attempt on the Khan's life by the Mongol warlord Tegana. Following this, Marco returned the TARDIS keys to their owners to allow their escape as Tegana's body was removed.

Barbara claimed that she knew that Polo would see Venice again, (TV: Marco Polo) although not before being captured by the Genoese. (PROSE: Marco Polo) Marco Polo did indeed return to Venice after 24 years of travelling to find the city at war with Genoa. Joining the war, Marco's ship was indeed captured by the Genoese and he was imprisoned. While in prison he dictated his stories to his cellmate who, the Twelfth Doctor noted, gave them some embellishment. The Travels of Marco Polo was published circa 1300. (PROSE: A History of Humankind)

Iris Wildthyme once held a party in Hobbe's End in 1972, which Marco Polo attended. (PROSE: From Wildthyme with Love)

Alternate timeline
In an alternate timeline, Polo purchased the Pandorica. As always, an Auton reconstruction of Amy Pond's fiancé, Rory Williams, accompanied the box. (TV: The Big Bang)

Minor references
The Doctor remarked to Susan once that they had saved Polo's life numerous times. (AUDIO: The Alchemists)

The Second Doctor recalled having met him. (TV: The Power of the Daleks)

Astrolabus claimed he had an appointment in Cathay with Marco Polo. (COMIC: Voyager)

By 1937, a bridge in northern China was named after him. (PROSE: The Shadow of Weng-Chiang)

The Thirteenth Doctor mentioned her previous journey with Marco Polo to Yasmin Khan. (COMIC: The White Dragon)

Behind the scenes

 * Marco Polo offers a clear example of how Doctor Who universe history differs from real-world history. According to real-world history, Polo was born in 1254. However, the first episode of Marco Polo explicitly tells us that he turned twenty-five in 1277, meaning that in the Doctor Who universe Marco Polo was born in 1252.
 * In Mags L. Halliday's The Silk Road, published in the fanzine Myth Makers Presents: Essentials in 2003, the Eighth Doctor, Fitz Kreiner, and Anji Kapoor accidentally spur Kublai Khan's decision to keep the younger Polo in his service in the first place. The story gives Polo a prior familiarity with the Doctor's "magic box," and shows the Doctor and Fitz undergoing a similar journey that the First Doctor, Susan, Ian, and Barbra would later experience with Polo.
 * In the story of Doctor Who: Legacy, the Seventh Doctor, stressing the importance of preventing the Sontarans' interference in the timeline, cites Marco Polo as an example of an important person in human history whose existence is endangered.
 * Marco Polo was first real person to be depicted in Doctor Who.