Jean-Guy "John" Kastner is a Canadian musician and composer born in Beaconsfield, Quebec. He was the singer for Montreal hardcore punk band the Asexuals as well as singer-guitarist for Montreal alternative band Doughboys and alternative band All Systems Go!. He is also the manager and former rhythm guitarist for the band Men Without Hats.

The Asexuals is a hardcore punk band from Beaconsfield that was a mainstay of the Montreal punk scene in the 1980s before changing into an alternative band following the departure of singer John Kastner. Kastner left to form the Doughboys and later, All Systems Go!.