Arnold Harris Mathew, self-styled de jure 4th Earl Landaff of Thomastown (7 August 1852 – 19 December 1919), was the founder and first bishop of the Old Catholic Church in the United Kingdom and a noted author on ecclesiastical subjects.
Mathew had been both a Roman Catholic and an Anglican before becoming a bishop in the Union of Utrecht (UU).
His early life is the subject of some interest from researchers as a result of his aristocratic connections and his father's connection with colonial India.