AC4 was a Swedish hardcore punk band from Umeå. Refused members Dennis Lyxzén and David Sandström had been talking about starting a new band for a long time. In the spring of 2008 Karl Backman had written songs for the new band and they started to rehearse. Jens Nordén had played with Lyxzén in pre-Refused straight edge hardcore band Step Forward (1987–1991) and since 1990 with Backman in punk band The Vectors. The "AC" in the name is the regional code for the Västerbotten province where Umeå is located.