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 on account of his dress style. (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.