Christopher Isherwood
From Tardis Wiki, the free Doctor Who reference
Christopher Isherwood (1904-1986) was an Anglo-American writer known for his novels and plays. He is also remembered as a long-time collaborator with poet W.H. Auden.
Jack Harkness claims to have once known Isherwood, to the point where the two went "cruising" together in the 1960s. His memory of Isherwood was sparked by Martha Jones quoting the title of one of Isherwood's best-known works, the play I Am a Camera. (TW: Reset)