Matthew William Tansley Stiff, formerly credited as Matt Stiff, is an English opera singer and former radio presenter, best known as the former bass singer with classical boyband G4.

G4 are a four-piece British vocal troupe who first came to prominence when they finished second in Series 1 of The X Factor in 2004, and are known for their operatic delivery of modern pop songs. Originally a barbershop quartet, the members met at the Guildhall School of Music and Drama, from which the name G4, standing for "Guildhall 4", derives.