William James Mathias CBE (1 November 1934 – 29 July 1992) was a Welsh composer noted for choral works.
At Aberystwyth University Mathias was a member of the Elizabethan Madrigal Singers and wrote 'Gloria in Excelsis Deo' for them in 1954.
Much of his music was written for the Anglican choral tradition, most famously the anthem Let the people praise Thee, O God written for the July 1981 royal wedding of the Prince and Princess of Wales, which had a television audience of an estimated 1 billion people worldwide.
The LSSO made the first commercial recording of Sinfonietta for the Pye Golden Guinea label in July 1967 under the direction of the composer (see external links below).
He founded the North Wales International Music Festival in St Asaph in 1972 and directed it until his death, aged 57, in 1992.