Marcellus Purnell Castle MVO, JP (1849–1917), known as M.P. Castle, was a British philatelist who was President of the Royal Philatelic Society London from 1913 to 1917, the first editor of The London Philatelist from 1892–1917 and whose name was entered on the Roll of Distinguished Philatelists as one of the "Fathers of philately". He was also awarded with the Lindenberg Medal in 1909. Castle's collecting interests were in Australian States and Europe of which areas he created large collections. He won a Gold medal for his display of New South Wales at the London Philatelic Exhibition 1890.