Karl Marx

Karl Heinrich Marx was a figure central to communism who wrote the major work Das Kapital. (PROSE: History 101; AUDIO: Brotherhood of the Daleks) The Doctor met Marx prior to or during his sixth incarnation. (AUDIO: Brotherhood of the Daleks) He had once lent his reader's ticket for the British Museum to Marx. (PROSE: Timewyrm: Apocalypse)

After his death, Marx was buried in Highgate Cemetery. (COMIC: The Highgate Horror)

Marxism was the political ideology promoted by Marx. (PROSE: History 101, TV: The Empty Child)

Behind the scenes
In The Sun Makers, Mandrel and the Fourth Doctor have the exchange, "What have we got to lose?" "Only your claims". This riffs on a common paraphrase of the final lines of by Marx and Friedrich Engels, "What have you got to lose? Only your chains." The official English translation of the line is "The proletarians have nothing to lose but their chains."

Joel Fry played Karl Marx in the BBC comedy series and its follow-up.