Gaston Marie Dethier (1875 – 1958) was an American organist, pianist, and composer of Belgian birth.

He was awarded premiers prix in organ, piano, harmony, and fugue from the conservatory.

[2] In 1886, at just 11 years of age, Dethier was appointed organist at the Église Saint-Jacques-le-Mineur de Liège.

He eventually left there to work in the same capacity at the Église Saint-Christophe de Liège.

Among his notable pupils were Ray Lev, Marcelle Martin, Carl McKinley, Georges-Émile Tanguay, and Powell Weaver.