Mary Cowles Clark (1871 – 1950) was the artist who illustrated the first edition of L. Frank Baum's The Life and Adventures of Santa Claus in 1902.
She was born in Syracuse, New York, and studied with the Art Students League. Baum had once lived in Syracuse, and met Mrs. Clark when visiting relatives there. It is thought that Baum personally chose Clark as his Santa Clause illustrator.
In her later years Mrs. Harlow Clark was associated with the Nantucket Arts Colony (1920–45); she spent summers painting in Siasconset, on the island's eastern shore.
She illustrated relatively few other books, apart from the Baum volume.
Source: Oz Wiki, "Mary Cowles Clark", available under the CC-BY-SA License.