William John Warner (also self-identified as Count Louis le Warner de Hamon), popularly known as Cheiro (1 November 1866 – 8 October 1936), was an Irish astrologer and colourful occult figure of the early 20th century. His sobriquet, Cheiro, derives from the word cheiromancy, meaning palmistry. He was a self-described clairvoyant who said he learned palmistry, astrology, and Chaldean numerology in India. He was celebrated for using these forms of divination to make personal predictions for famous clients and to foresee world events.

The son of William Warner and Margaret Thompson Warner, Cheiro was born William John Warner in the barony of Rathdown, outside Dublin, Ireland. He took the name Count Louis Hamon (or Count Leigh de Hamong).

As mentioned in his memoirs, Cheiro acquired his expertise in India. As a teenager, he travelled to the Bombay port of Apollo Bunder. There, he wrote that he met his guru, an Indian Chitpavan Brahmin, who took him to his village in the valley of the Konkan region of Maharashtra. Later Cheiro was permitted by Brahmans to study an ancient book that has many studies on hands. After studying thoroughly for two years, he returned to London and started his career as a palmist.

In 1920 he married Mrs. Katie Hartland.

Cheiro had a wide following of famous European and American clients during the late 19th and early 20th centuries. He read palms and told the fortunes of famous celebrities like Mark Twain, W. T. Stead, Sarah Bernhardt, Mata Hari, Oscar Wilde, Grover Cleveland, Thomas Edison, the Prince of Wales, General Kitchener, William Ewart Gladstone, and Joseph Chamberlain. He documented his sittings with these clients by asking them to sign a guest book he kept for the purpose, in which he encouraged them to comment on their experiences as subjects of his character analyses and predictions. Of the Prince of Wales, he wrote that "I would not be surprised if he did not give up everything, including his right to be crowned, for the woman he loved." Cheiro also predicted that the Jews would return to Palestine and the country would again be called Israel.

In his own autobiographical book, Cheiro's Memoirs: The Reminiscences of a Society Palmist, he included accounts of his interviews with King Edward VII, William Gladstone, Charles Stewart Parnell, Henry Morton Stanley, Sarah Bernhardt, Oscar Wilde, Professor Max Muller, Blanche Roosevelt, the Comte de Paris, Joseph Chamberlain, Lord Russell of Killowen, Robert Ingersoll, Ella Wheeler Wilcox, Lillie Langtry, W. T. Stead, Richard Croker, Natalia Janotha, and other prominent people of his era.

The book Titanic's Last Secrets includes a detailed account of one of Cheiro's palm readings with William Pirrie, chairman of Harland and Wolf, builders of the Titanic. Cheiro predicted that he would soon be in a fight for his life, talking about the battle surrounding the Titanic sinking.

It becomes a study not contrary to the dictates of reason, but in accordance with those natural laws that we observe in the shaping of the even inanimate objects, which, by demonstrating the effect of a heretofore cause, are in themselves the cause of a hereafter effect. – Cheiro