John Mogensen (May 5, 1928 – April 10, 1977) was a Danish singer, songwriter and pianist.
He was a member of the song quartet Four Jacks (1956-1963) and already then getting popularity as a song writer but after some years he had a remarkable come back as a solo singer from 1971. With his rough voice and frank and direct language he formed a rare link between traditional pop and the folk song, alternating between direct criticism of society, simple love songs and reflections from the pub milieu that he knew so well. Several of his songs are still well known today, for example Der er noget galt i Danmark, Så længe jeg lever, and Fut i fejemøjet.
After his early death he was almost a cult figure to many enthusiasts, his songs have been re-issued and even a musical based upon his daily life went on for several years.