Pierre De Geyter was a Belgian-French socialist composer, known for composing the tune of "The Internationale" in 1888, which had been previously sung to the tune of "La Marseillaise".
It took him one morning to compose the tune of "The Internationale" on a harmonium. The new composition was first played by the Lyre des Travailleurs at the yearly fête of the Lille trade union of newspaper sellers in July 1888.