Stef Caers (Dutch pronunciation: ; born 5 July 1980), known professionally as Gustaph (stylised as GVSTΛPH), is a Belgian singer-songwriter, producer and vocal coach. He is set to represent Belgium in the Eurovision Song Contest 2023 in Liverpool, United Kingdom with the song "Because of You".
Caers was born on 5 July 1980 in Leuven, Flemish Brabant. He started his musical career while studying at the Royal Conservatory of Ghent, initially using the stage name Steffen. In 2000, he scored a hit with his debut single "Gonna Lose You", which reached number 22 on the Flemish singles chart. He subsequently released a second single, titled "Sweetest Thing".
Following these releases, Caers began focusing more on songwriting and producing. He also became active as a backing vocalist, providing backing vocals for, among others, Lady Linn and Willy Sommers. In the early 2010s, he joined the band Hercules and Love Affair as one of the lead vocalists.