In The Wasteland (1922), T S Eliot makes a reference to Ernest Shackleton's South, published in 1919. In this account of the extreme circumstances of their trek across South Georgia in search of rescue, Shackleton and his two companions felt frequently that they were in the presence of another.
This story reappeared in Eliot's poem and then surfaced irregularly in the psychology of trauma as the Third Man Factor or the Sensed Presence Effect.
Who is the third who walks always beside you?
When I count, there are only you and I together
But when I look ahead up the white road
There is always another one walking beside you
Gliding wrapt in a brown mantle, hooded
I do not know whether a man or a woman
—But who is that on the other side of you?
Also relevant to Federated Wiki: Shackleton wrote his book South by dictating to a New Zealand ghost writer, Edward Saunders, with whom he had worked on a previous book.
"This was not unusual practice; many polar explorers had a horror of the dull mechanics involved in writing and it had been common since the 1850s for them to leave the job to a professional."
Related: Who's We, White Man?