William Cartheuser (January 19, 1890 – February 25, 1966) was an American spiritualist medium.

[1] In 1928, he conducted séances with the spiritualist Jenny O'Hara Pincock in Ontario, Canada.

[4][5] Pincock originally endorsed Cartheuser as a genuine medium but later broke connections, suggesting that he had turned his mediumship into a financial scheme.

He concluded that "a high percentage of fraud enters into the production of Cartheuser's physical phenomena.

"[6][7] Psychologist Henry C. McComas who observed Cartheuser at many sittings, detected his trickery.