Marty McFly

Marty McFly was, according to differing accounts, either a character in the Back to the Future series of films, (TV: The Shakespeare Code, etc.) or a real individual who was in proximity with the Doctor on various occasions. (WC: Doctor, Doctor, Doctor, New Adventures Await!, etc.)

Biography
On the website Doctor Who?, a user, going by the name Marty McFly, claimed to have seen the Ninth Doctor, saying "I know that man, he stole my DeLorean!!!". (PROSE: Have You Seen This Man?)

McFly was standing in the Brick Boulevard when the Twelfth Doctor, Doc Brown, and Peter Venkman crashed their vehicles into each other, winding up in a wreck. (WC: Doctor, Doctor, Doctor)

Later, he visited Diagon Alley, and jumped out of the way as Wyldstyle sped towards him on a motorcycle. He later charged into battle alongside several other individuals in the Land of Ooo, before winding up in a mosh pit with the rest of the battle's participants. (WC: New Adventures Await!)

Other references
The Tenth Doctor once used Marty McFly to illustrate the theory of infinite temporal flux to Martha. In the film, McFly "began to fade" out of existence as changes were made to his personal family history. This, the Doctor suggested, was indicative of the general malleability of time — and of what would happen to Earth's future if he and Martha could not stop the Carrionites in 1599. (TV: The Shakespeare Code)

Paul was a fan of Back to the Future and wore headphones, a T-shirt, checked shirt, denim jacket, body warmer, jeans, and trainers just like Marty McFly. (PROSE: The Sooner the Better)

Joel Mintz encountered a time rift which transported him from 1993 to 1983. He said he felt like Marty McFly when it came to TV reruns: "I've seen everything before." (PROSE: Return of the Living Dad)

Two cosplayers at San Diego Comic-Con dressed as Doc Brown and Marty McFly. (COMIC: Selfie)

The Eleventh Doctor made reference to Marty McFly and the Back to the Future series after giving an eponymous reference to the series to Alice Watson, which she didn't get due to her lack of interest in fiction. (AUDIO: The Time Machine)

The Twelfth Doctor used Back to the Future to try and explain a time travel situation that he and three versions of Bill Potts were in, mentioning Marty as knowing his dad as a loser despite his personal timeline changing to a state where that version of his father no longer existed. (AUDIO: Emancipation of the Daleks)

In non-valid sources
Marty McFly once played his red guitar, causing the Wicked Witch of the West to fall off of her broomstick. He later played it next to the DeLorean time machine. (WC: Endless Awesome)

Other matters
Marty, along with his Back to the Future costar Doc Brown, appears as a playable character in LEGO Dimensions.