Katie King was the name given by Spiritualists in the 1870s to what they believed to be a materialized spirit. The question of whether the spirit was real or a fraud was a notable public controversy of the mid-1870s.
The spirit was said to have appeared first between 1871 and 1874 in séances conducted by Florence Cook in London, and later in 1874-1875 in New York in séances held by the mediums Jennie Holmes and her husband Nelson Holmes.
Katie King was believed by Spiritualists to be the daughter of John King, a spirit control of the 1850s through the 1870s that appeared in many séances involving materialized spirits.
(A spirit control is a powerful and communicative spirit that organizes the appearance of other spirits at a séance. John King claimed to be the spirit of Henry Morgan, the buccaneer (Doyle 1926: volume 1, 241, 277).)
Florence Cook (ca 1856 – 1904) was a teenage girl who started to claim mediumistic abilities in 1870 and in 1871-2 she developed her abilities under the established mediums Frank Herne and Charles Williams. Herne was associated with the spirit "John King", and Florence became associated with "Katie King", stated to be John King's daughter. Herne was exposed as a fraud in 1875. Katie King developed from appearing as a disembodied face to a fully physical materialisation.
At Hackney on 9 December 1873, lawyer William Volckman attended a séance held by Florence Cook, during which Katie King materialized and, as was customary, held the hands of participants. Suspicious of the spirit's similarity with Cook, Volckman seized the spirit's hand and waist, accusing it of being the medium masquerading as her ghost. The spirit was wrestled from Volckman's grasp by other participants and returned to a cabinet from which Cook emerged some minutes later. Volckman published his opinion that the spirit was a masquerade by Cook. Supporters of Miss Cook denounced Volckman on the grounds that he had broken his agreement to proper etiquette required in the séance, thus negating his credibility as an investigator: Volckman was associated with another medium, Mrs Guppy, who might have wished to denigrate her rival. Moreover, it was argued that since spirits borrowed energy and matter from their medium, it was not surprising that Katie King resembled Cook. Despite the defence of their position, Cook and her supporters were hurt by this incident — newspapers were referring to it as an "exposure" — and sought further support for their position. To this end, they turned to Crookes, who was a prominent and respected scientist (Noakes, 130-1).