Red Baron

The Red Baron was a famous ace pilot.

He taught the Doctor to make a barrel roll. (PROSE: The Secret in Vault 13)

According to the Third Doctor, the Red Baron liked to approach his adversaries from the direction of the sun. (PROSE: Doctor Who and the Planet of the Spiders)

Jack Harkness was once compared to Red Baron by Allen Shapiro on account of his World War II coat, commenting "What is it with you, Red Baron? You got Snoopy up your ass?" (TV: End of the Road)

Behind the scenes
In the real world, "Red Baron" was a popular nickname of Manfred von Richthofen, a German ace pilot active in World War I. Several German military aviation squadrons were named after him. Some of them are mentioned in-universe. For instance, Hermann Goering is stated as "commander of the famous von Richthofen squadron" in the novel Timewyrm: Exodus. But no connection to the Red Baron is made there.

Shapiro's comment is a reference to a running gag in the Peanuts comic strip where Snoopy would battle the Baron.